[Federal Register: November 4, 2005 (Volume 70, Number 213)]
[Proposed Rules]
[Page 67277-67302]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr04no05-18]
[[Page 67277]]
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Part III
Department of Transportation
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Federal Aviation Administration
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14 CFR Part 25
Airplane Performance and Handling Qualities in Icing Conditions;
Proposed Advisory Circular 25.21-1X, Performance and Handling
Characteristics in the Icing Conditions Specified in Part 25, Appendix
C; Proposed Rule and Notice
[[Page 67278]]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. 2005-22840; Notice No. 05-10]
RIN 2120-AI14
Airplane Performance and Handling Qualities in Icing Conditions
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed rulemaking (NPRM).
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SUMMARY: This action proposes to introduce new airworthiness standards
to evaluate the performance and handling characteristics of transport
category airplanes in icing conditions. This proposed action would
improve the level of safety for new airplane designs when operating in
icing conditions, and would harmonize the U.S. and European
airworthiness standards for flight in icing conditions.
DATES: Send your comments on or before February 2, 2006.
ADDRESSES: You may send comments identified by Docket Number FAA-2005-
22840 using any of the following methods:
DOT Docket Web site: Go to http://dms.dot.gov and follow
the instructions for sending your comments electronically.
Government-wide Regulations and Policies Web site: Go to
http://www.faa.gov/regulations_policies/ and follow the instructions
for sending your comments electronically.
Mail: Docket Management Facility; U.S. Department of
Transportation, 400 Seventh Street, SW., Nassif Building, Room PL-401,
Washington, DC 20590-001.
Fax: 1-202-493-2251.
Hand Delivery: Room PL-401 on the plaza level of the
Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
For more information on the rulemaking process, see the
SUPPLEMENTARY INFORMATION section of this document.
Privacy: We will post all comments we receive, without change, to
http://dms.dot.gov, including any personal information you provide. For
more information, see the Privacy Act discussion in the SUPPLEMENTARY
INFORMATION section of this document.
Docket: To read background documents or comments received, go to
http://dms.dot.gov at any time or to Room PL-401 on the plaza level of
the Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
FOR FURTHER INFORMATION CONTACT: Don Stimson, FAA, Airplane & Flight
Crew Interface Branch, ANM-111, Transport Airplane Directorate,
Aircraft Certification Service, 1601 Lind Avenue SW., Renton, WA 98055-
4056; telephone: (425) 227-1129; fax: (425) 227-1149, e-mail:
don.stimson@faa.gov.
SUPPLEMENTARY INFORMATION:
Comments Invited
The FAA invites interested persons to participate in this
rulemaking by submitting written comments, data, or views. We also
invite comments relating to the economic, environmental, energy, or
federalism impacts that might result from adopting the proposals in
this document. The most helpful comments reference a specific portion
of the proposal, explain the reason for any recommended change, and
include supporting data. We ask that you send us two copies of written
comments.
We will file in the docket all comments we receive, as well as a
report summarizing each substantive public contact with FAA personnel
concerning this proposed rulemaking. The docket is available for public
inspection before and after the comment closing date. If you wish to
review the docket in person, go to the address in the ADDRESSES section
of this preamble between 9 a.m. and 5 p.m., Monday through Friday,
except Federal holidays. You may also review the docket using the
Internet at the Web address in the ADDRESSES section.
Privacy Act: Using the search function of our docket Web site,
anyone can find and read the comments received into any of our dockets,
including the name of the individual sending the comment (or signing
the comment of behalf of an association, business, labor union, etc.).
You may review DOT's complete Privacy Act statement in the Federal
Register published on April 11, 2000 (65 FR 19477-78) or you may visit
http://dms.dot.gov.
Before acting on this proposal, we will consider all comments we
receive on or before the closing date for comments. We will consider
comments filed late if it is possible to do so without incurring
expense or delay. We may change this proposal in light of the comments
we receive.
If you want the FAA to acknowledge receipt of your comments on this
proposal, include with your comments a pre-addressed, stamped postcard
on which the docket number appears. We will stamp the date on the
postcard and mail it to you.
Availability of Rulemaking Documents
You can get an electronic copy using the Internet by:
(1) Searching the Department of Transportation's electronic Docket
Management System (DMS) Web page (http://dms.dot.gov/search); (2) Visiting the Office of Rulemaking's Web page at http://
http://www.faa.gov/avr/arm/index.cfm; or
(3) Accessing the Government Printing Office's Web page at http://www.gpoaccess.gov/fr/index.html
.
You can also get a copy by sending a request to the Federal
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence
Avenue SW., Washington, DC 20591, or by calling (202) 267-9680. Make
sure to identify the docket number, notice number, or amendment number
of this rulemaking.
Authority for This Rulemaking
The FAA's authority to issue rules regarding aviation safety is
found in Title 49 of the United States Code. Subtitle I, section 106
describes the authority of the FAA Administrator. Subtitle VII,
Aviation Programs, describes in more detail the scope of the agency's
authority.
This rulemaking is promulgated under the authority described in
subtitle VII, part A, subpart III, section 44701, ``General
requirements.'' Under that section, the FAA is charged with promoting
safe flight of civil aircraft in air commerce by prescribing minimum
standards required in the interest of safety for the design and
performance of aircraft. This regulation is within the scope of that
authority because it prescribes new safety standards for the design of
transport category airplanes.
Organization of This NPRM
Discussion of this proposal is organized under the headings listed
below. Whenever there is a reference to a document being included in
the docket for this NPRM, the docket referred to is Docket Number FAA-
2005-22840. A list of acronyms used is included in an appendix located
at the end of the preamble material, between the regulatory evaluation
and the text of the proposed amendments. Unless stated otherwise, rule
sections referenced in this NPRM are part of Title 14, Code of Federal
Regulations (14 CFR).
I. Executive Summary
If adopted, this rulemaking would revise certain sections of part
25 of Title
[[Page 67279]]
14 Code of Federal Regulations (14 CFR). Part 25 contains the
airworthiness standards for type certification of transport category
airplanes, but it does not currently include specific requirements for
airplane performance or handling qualities for flight in icing
conditions. Although part 25 requires airplanes with approved ice
protection features to be able to operate safely in icing conditions,
there is no standard set of criteria defining what ``to safely
operate'' in icing conditions means in terms of airplane performance
and handling qualities. Further, because the existing icing regulations
only address airplanes with ice protection provisions, it is unclear
what requirements apply in cases where the applicant is seeking to have
an airplane without an ice protection system certificated for flight in
icing conditions.
This notice proposes to amend part 25 by adding a comprehensive set
of airworthiness requirements that must be met to receive certification
approval for flight in icing conditions, including specific performance
and handling qualities requirements, and the ice accretion (that is,
the size, shape, location, and texture of the ice) that must be
considered for each phase of flight. These proposed revisions would
ensure that minimum operating speeds determined during the
certification of all future transport category airplanes would provide
adequate maneuver capability in icing conditions for all phases of
flight and all airplane configurations.
This notice proposes to require the same airplane handling
characteristics that apply in non-icing conditions to continue to apply
in icing conditions. Additionally, a specific evaluation for
susceptibility to tailplane stall in icing conditions would be added.
This proposal, if adopted, would harmonize the U.S. and European
airworthiness standards for flight in icing conditions. It would
benefit the public interest while retaining or enhancing the current
level of safety for operation in icing conditions.
If adopted, this rulemaking would affect manufacturers, modifiers,
and operators of transport category airplanes (but only for new designs
or significant changes to current designs that would affect the safety
of flight in icing conditions). Manufacturers and modifiers may need to
develop new tests and analyses to determine ice accretions and to
estimate performance effects for design and certification to address
icing conditions. Operators may need to develop new or revised
procedures regarding identification of icing conditions and the
operation of the ice protection system.
Service history shows that flight in icing conditions may be a
safety risk for transport category airplanes. There have been nine
accidents since 1983 that may have been prevented if this proposed rule
had been in effect.\1\ The service history that we examined includes
airplanes certificated to part 25, to its predecessor, the Civil Air
Regulations (CAR) 4b, or to part 25 icing standards when the airplane
was certified under part 23. In evaluating the potential for this
rulemaking to avoid future accidents, we only considered past accidents
involving tailplane stall or potential airframe ice accretion effects
on drag or controllability. Accidents related to ground deicing were
not considered.
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\1\ These accidents were selected from the National
Transportation Safety Board's (NTSB) accident database, and are
discussed in Appendix 3 of this premable.
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The NTSB has issued several safety recommendations related to
airframe icing, some of which are addressed, at least in part, by this
notice. If adopted, this rulemaking would require, during type
certification, that manufacturers of transport category airplanes:
Investigate the susceptibility of their airplanes to ice-
contaminated tailplane stall (ICTS);
Provide for adequate warning on the flight deck of an
impending stall in icing conditions;
Show that their airplanes meet the same maneuvering
capability and handling characteristics requirements in icing
conditions as in non-icing conditions; and
Show that their airplanes have adequate performance
capability in icing conditions.
As discussed in more detail later, the FAA has tentatively
determined that this rulemaking would have the following costs and
benefits over a 45-year analysis period. The cost of the proposed rule
would be $22.0 million (present value). The FAA assumes the initial
certification costs of $6.7 million for four new airplane models are
incurred in year one of a 45-year analysis period. The future
additional fuel burn expense is estimated to be $59.7 million and would
be incurred over the 45-year analysis period. The benefits of this
proposed rule consist of the value of lives saved due to avoiding
accidents involving part 25 airplanes operating in icing conditions.
Over the 45-year period of analysis, the potential benefit of the
proposed rule would be $89.9 million ($23.7 million in present value at
seven percent).
A. Past Regulatory Approach
Currently, Sec. 25.1419, ``Ice protection,'' requires transport
category airplanes with approved ice protection features be capable of
operating safely within the icing conditions identified in appendix C
of part 25. This section also requires flight testing and analyses to
be performed to make this determination. Although an airplane's
performance capability and handling qualities are important in
determining whether an airplane can operate safely, part 25 does not
have specific airplane performance or handling qualities requirements
for flight in icing conditions, nor does the FAA have a standard set of
criteria defining what ``to safely operate'' in icing conditions means
in terms of airplane performance and handling qualities. The proposed
revisions to part 25 would provide a comprehensive set of harmonized
requirements for airplane performance and handling qualities to address
safe operation of transport category airplanes in icing conditions.
Further, Sec. 25.1419 requires an applicant to demonstrate that
the airplane can operate safely in icing conditions only when the
applicant is seeking to certificate ice protection features. It fails
to address certification approval for flight in icing conditions for
airplanes without ice protection features.
In contrast, the European airworthiness standards specifically
address certification for flight in icing conditions, independent of
whether the airplane includes ice protection features. In addition, the
European Joint Aviation Authorities (JAA) proposed additional guidance
material in the early 1990s to provide criteria for determining whether
an airplane's performance and handling qualities would allow the
airplane to operate safely in icing conditions. The JAA's guidance
material was proposed in draft Advisory Material--Joint (AMJ)
25.1419.\2\ The JAA's draft AMJ was published on April 23, 1993, as a
Notice of Proposed Amendment (NPA) 25F-219, ``Flight in Icing
Conditions--Acceptable Handling Characteristics and Performance
Effects.''
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\2\ A JAA AMJ is similar to an FAA advisory circular.
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B. Harmonization of U.S. and European Regulatory Standards
1. Federal Aviation Administration
Title 14 CFR part 25 contains the U.S. airworthiness standards for
type certification of transport category airplanes. The part 25
standards apply to airplanes manufactured within the
[[Page 67280]]
U.S. and to airplanes manufactured in other countries and imported to
the U.S. under a bilateral airworthiness agreement.
2. Joint Aviation Authorities
The JAR-25 contains the European airworthiness standards for type
certification of transport category airplanes. Thirty-seven European
countries accept airplanes type certificated to the JAR-25 standards,
including airplanes manufactured in the U.S. that are type certificated
to JAR-25 standards for export to Europe.
3. European Aviation Safety Agency (EASA)
The European Community established a new aviation regulatory body,
EASA, to develop standards to ensure the highest level of safety and
environmental protection, oversee their uniform application across
Europe, and promote them internationally. The EASA formally became
operational for certification of aircraft, engines, parts, and
appliances on September 28, 2003. The EASA will eventually absorb all
of the functions and activities of the JAA, including its efforts to
harmonize the European airworthiness certification regulations with
those of the U.S.
The JAR-25 standards have been incorporated into the EASA's
``Certification Specifications for Large Aeroplanes,'' (CS)-25, in
similar if not identical language. The EASA's CS-25 became effective
October 17, 2003.
The proposals contained in this notice were developed in
coordination with the JAA. However, since the JAA's JAR-25 and the
EASA's CS-25 are essentially the same, all of the discussions of these
proposals relative to JAR-25 also apply to CS-25.
The FAA's rulemaking proposal, if adopted, would parallel the JAA's
rulemaking proposal, ``Notice of Proposed Amendment (NPA) 25B, E, F-
332,'' published on June 1, 2002.
The EASA recently published for comment NPA 16/2004, ``Draft
Decision of the Executive Director of the Agency on Certification
Conditions.'' This NPA, published for comment in late 2004, is based on
the standards that the JAA were expected to adopt.
Although the FAA, the JAA, and EASA intend to harmonize the
standards for airplane performance and handling qualities for flight in
icing conditions, there are some differences between this rulemaking
proposal and the standards proposed by the JAA and EASA. The
differences are primarily editorial and are not intended to result in
significant regulatory differences.
C. Proposal Development--Aviation Rulemaking Advisory Committee
The FAA, in cooperation with the JAA and representatives of the
American and European aerospace industries, recognized that a common
set of standards would not only economically benefit the aviation
industry, but also maintain a high level of safety. In 1988, the FAA
and the JAA began a process to harmonize their respective airworthiness
standards. To assist in the harmonization efforts, the FAA established
the Aviation Rulemaking Advisory Committee (ARAC) in 1991,\3\ to:
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\3\ Published in the Federal Register (56 FR 2190), on January
22, 1991.
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1. Provide advice and recommendations concerning the full range of
our safety-related rulemaking activity;
2. Develop better rules in less overall time using fewer FAA
resources than are currently needed; and
3. Obtain firsthand information and insight from interested parties
regarding proposed new rules or revisions of existing rules.
There are 73 member organizations on the committee, representing a wide
range of interests within the aviation community.
We tasked the ARAC Flight Test Harmonization Working Group (FTHWG)
to recommend to the ARAC new or revised requirements and compliance
methods related to airplane performance and handling qualities in icing
conditions.\4\
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\4\ Published in the Federal Register (56 FR 2190), on June 10,
1994.
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The FTHWG reviewed in-service incidents and accidents involving
transport category airplanes. This review revealed numerous incidents
resulting from the effects of ice on airplane performance. The same
review showed that the icing-related accidents resulted from a loss of
control of the airplane due to the effect of the ice on airplane
handling qualities. Considering this service history, the FTHWG
determined that airplanes should generally meet the same handling
qualities standards in icing conditions that they currently must meet
for non-icing conditions. In certain areas, however, the FTHWG decided
that the current handling qualities standards were inappropriate for
flight in icing conditions. In these areas, the FTHWG developed
alternative criteria that would apply to icing conditions.
Since airplane performance degradation was not a causal factor in
any of the icing-related accidents, the FTHWG concluded that the
current performance standards already provide some safety margin to
offset the negative effects of ice accretion. On the basis of this
service history, the FTHWG decided that the general approach to
airplane performance in icing conditions used by the JAA in their draft
AMJ 25.1419 was appropriate and used this approach in its
recommendations to the FAA. This approach allows a limited reduction in
airplane performance capability due to ice before the effects of icing
must be fully taken into account in the performance data provided in
the Airplane Flight Manual (AFM). Such an approach minimizes the costs
to manufacturers and operators while increasing the current level of
safety for flight in icing conditions.
This proposed rulemaking is based on the FTHWG's report, which ARAC
approved and forwarded to the FAA, and refers to the ice accretions to
be used in showing compliance. These ice accretions are defined in a
new subsection of appendix C to part 25.\5\
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\5\ The complete text of the FTHWG's report is available at
http://www.faa.gov/avr/arm/arac/aractasks/fr0404report.pdf. The
FTHWG preferred the term ``ice accretion'' rather than ``ice shape''
because it includes physical characteristics of the ice build-up
such as texture and surface roughness in addition to its general
size and shape.
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D. Related Rulemaking Activity
1. Amendment 25-108
This Amendment, ``1-g Stall Speed as the Basis for Compliance With
Part 25 of the Federal Aviation Regulations'' (referred to as the 1-g
stall rule) (67 FR 708112, November 26, 2002) redefines the criteria
for determining the stall speed for transport category airplanes. The
stall speed is important because it is used as a reference speed for
defining minimum operating speeds that provide a safety margin above
the speed at which the airplane will stall. The previous part 25
definition of stall speed defined it as the minimum speed reached in a
stalling maneuver. This definition could result in a stall speed being
defined that is too low to support the weight of the airplane in level
flight.
The recently adopted 1-g stall rule defines the stall speed as the
speed at which the aerodynamic lift can support the weight of the
airplane in 1-g flight. The 1-g stall rule also introduces a
requirement to demonstrate adequate maneuver capability at the minimum
operating speeds for airplane configurations associated with low speed
operations around airports. The JAA adopted the same 1-g stall speed
requirements in Change 15 to JAR-25.
[[Page 67281]]
2. Ice Protection Harmonization Working Group (IPHWG) Recommendations
The FAA tasked the ARAC to consider whether airplane manufacturers
or operators should be required to install ice detectors or provide
some other acceptable way to warn flightcrews of potentially unsafe ice
accumulations. The ARAC assigned this task to the IPHWG. The IPHWG
recommended to the ARAC that the FAA adopt an operating rule for
certain types of airplanes that would require a reliable method of
informing pilots when to activate the ice protection system as well as
a way of knowing when ice is accumulating aft of areas protected by the
ice protection system. The IPHWG is also working on a recommendation
for a type certification requirement that would identify acceptable
ways to inform the flightcrew when to activate the ice protection
system.
We also tasked the ARAC to:
Define an icing environment that includes supercooled
large drop (SLD) icing conditions;
Recommend requirements to assess the ability of aircraft
to safely operate in SLD icing conditions, either for the period of
time necessary to exit or to operate without restriction; and
Consider mixed phase conditions (a mixture of supercooled
water droplets and ice crystals) if such conditions are more hazardous
than the liquid phase icing environment containing supercooled water
droplets.
When ARAC finishes its tasks, we expect it to forward to us a
report containing their recommendations. These recommendations may lead
to future rulemaking to address SLD icing conditions, but would not
directly impact this rulemaking.
E. Advisory Material
In addition to being tasked to recommend new or revised
requirements related to airplane performance and handling qualities in
icing conditions, the ARAC FTHWG was tasked to recommend advisory
material identifying acceptable ways to comply with the proposed new or
revised requirements. The FTHWG developed a proposed Advisory Circular,
(AC) 25.21-1X, ``Performance and Handling Characteristics in the Icing
Conditions Specified in Part 25, Appendix C.'' We are requesting public
comments on this proposed advisory circular through a separate notice
of availability in this edition of the Federal Register.
II. Discussion of the Proposals
A. Proof of Compliance (Sec. 25.21)
We propose to add paragraph (g), to specify the requirements that
must be met in icing conditions if an applicant seeks certification
approval for flight in icing conditions. As discussed above, a review
of icing-related incidents and accidents revealed loss of control to be
the greatest threat to safety of flight in icing conditions.
Consequently, the FTHWG identified the existing part 25 requirements
that could prevent loss of control if they were applied to icing
conditions. The FTHWG found, and we tentatively agree, that airplanes
should continue to comply with most of subpart B of part 25 with ice on
the airplane to ensure safe flight in icing conditions. The subpart B
regulations that would be excluded by paragraph (g)(1) were determined
to be beyond what was necessary to determine an airplane's ability to
operate safely in icing conditions.
Because the airplane performance and handling qualities
requirements are flight-related requirements, it is appropriate to
place the proposed requirements for flight in icing conditions in part
25, subpart B (Flight) rather than in the current ice protection rule
in Sec. 25.1419. Section 25.1419 is in subpart F (Equipment), and,
though it is closely linked with the subpart B requirements proposed in
this notice, it primarily applies to the ice protection equipment on
the airplane.
The proposed subpart B requirements would provide the minimum
performance and handling qualities requirements corresponding to the
Sec. 25.1419 requirement that the airplane ``be able to safely operate
in the continuous maximum and intermittent maximum icing conditions of
appendix C.'' Additionally, the proposed requirements would supply the
means for determining, from a performance and handling qualities
standpoint, whether the ice protection system and its components are
effective, as required by Sec. 25.1419(b).
Compliance with the proposed performance and handling qualities
requirements may be shown by a variety of means that would be evaluated
during the particular airplane type certification program. These means
may include flight testing in natural icing conditions or in non-icing
conditions using artificial ice shapes, wind tunnel testing and
analysis, engineering simulator testing and analysis, engineering
analysis, and comparison to previous similar airplanes.
The proposed requirements would not specifically require
performance and handling qualities flight testing to be conducted in
natural icing conditions. However, we expect that for most new airplane
designs, and for significant changes to existing designs, at least a
limited set of tests would be flown in natural icing conditions. The
purpose of these tests would be to confirm the airplane handling
qualities and performance results found through other means. The
proposed advisory material will provide guidance on an acceptable
flight test program, including the specific tests that should be
conducted in natural icing conditions.
Historically, flight tests in measured natural icing conditions
have also been conducted to verify analyses used to generate ice
accretions for compliance with Sec. 25.1419(b), and to confirm the
general physical characteristics and location of ice accretions used to
evaluate airplane performance and handling qualities. This proposed
rule is not intended to alter this practice or interpretation of Sec.
25.1419(b). Existing AC 25.1419-1, ``Certification of Transport
Category Airplanes for Flight in Icing Conditions,'' provides guidance
on comparing the ice accretions used to evaluate airplane performance
and handling qualities with those obtained in natural icing conditions.
Proposed paragraph (g)(1) would apply the same airplane handling
qualities requirements to flight in icing conditions as are currently
required for non-icing conditions. Paragraph (g)(1) would also apply
most of the airplane performance requirements currently required for
non-icing conditions to flight in icing conditions. The icing
conditions for showing compliance would be defined in appendix C to
part 25. These requirements would apply to normal operations of the
airplane and its ice protection system as specified in the AFM. By
referencing the AFM, this paragraph would require that this manual
include the limitations and operating procedures that are specific to
operating in icing conditions.
As noted in the introductory discussion, some degradation in
airplane performance capability would be permitted when showing
compliance with the requirements for non-icing conditions. The amount
of performance degradation permitted in each case is identified in the
discussion of the individual performance regulations.
Proposed paragraph (g)(2) would prevent the use of different load,
weight, and center-of-gravity limits for flight in icing, except where
compliance with the applicable performance requirements impose more
restrictive weight limits.
The reason for these proposed requirements is that operation in
icing
[[Page 67282]]
conditions should be essentially transparent to the flightcrew. There
should not be any special procedures or methods used for operating in
icing conditions other than activating ice protection systems. This
philosophy comes from applying human factors principles to reduce
operational complexity and flightcrew workload.
B. Stall Speed (Sec. 25.103)
We propose to revise Sec. 25.103 to require applicants to
determine stall speeds with ice on the airplane. The proposed Sec.
25.103(b)(3) adds ice accretion as a variable that must be considered
when determining stall speeds to use for the different part 25 airplane
performance standards.
Determining stall speeds with ice accretions is necessary to
identify any increase in stall speeds from those determined for non-
icing conditions. The applicant would then compare any change in stall
speed due to ice accretion with the allowable stall and operating speed
effects contained in the proposed airplane performance standards to
determine whether or not airplane performance data must be determined
specifically for icing conditions.
C. Takeoff (Sec. 25.105)
We propose to revise Sec. 25.105(a) to add the net takeoff flight
path described in Sec. 25.115 to the list of airplane takeoff
performance parameters that must be determined under the conditions
specified in this paragraph. Additionally, Sec. 25.105(a) would
specify when compliance must be shown specifically for icing
conditions.
We consider the proposed changes necessary to ensure the safety of
takeoff operations in icing conditions. Ice on the wings and control
surfaces can reduce the safety margins that currently are provided to
prevent stalling the airplane. It can also degrade airplane climb
performance, and cause controllability problems. We acknowledge that
many transport category airplanes have safely operated in icing
conditions using takeoff speeds determined for non-icing conditions. We
agree with the FTHWG, however, that it is in the interest of safety to
consider the effects of ice accretions on airplane takeoff performance.
In developing this proposal, the FTHWG and the FAA considered four
factors:
Operating rules and practices intended to ensure that
critical surfaces of the airplane are free of snow or ice before
beginning a takeoff;
The use of anti-icing fluids that provide some protection
from icing during the takeoff;
Increasing use of ice detectors and deicing/anti-icing
systems on airplanes that can be operated while the airplane is still
on the ground; and
The icing conditions that we propose to use for the
takeoff flight phase.
Existing operating rules, Sec. Sec. 91.527(a), 121.629(b), and
135.227(a), prohibit pilots from taking off with snow or ice adhering
to the wings or other critical airplane surfaces. Additionally,
Sec. Sec. 121.629(c) and 135.227(b) require airplane operators to have
either an approved ground deicing/anti-icing program or conduct a pre-
takeoff contamination check within five minutes before beginning a
takeoff to ensure that the wings, control surfaces, and other critical
surfaces are free of frost, ice, or snow. Operators must train the
pilots on the effects of these contaminants on airplane performance and
controllability, on how to recognize airplane contamination, and on
procedures intended to ensure that contamination is removed before
takeoff.
Ground deicing/anti-icing programs include the use of deicing/anti-
icing fluids to remove ice and snow and prevent them from reappearing
on airplane surfaces during freezing precipitation conditions. Although
these fluids are designed to flow off the airplane during the takeoff
roll, we expect the fluids to continue to provide some protection
throughout the takeoff ground run.
On some older airplane models, the wing ice protection system was
designed for use in flight and cannot be operated while the airplane is
on the ground. Yet many of the current generation of airplanes have ice
protection systems that can be operated while the airplane is on the
ground. Some of these systems are also coupled with ice detector
systems that will automatically activate the ice protection system in
icing conditions. These features tend to reduce the chances that ice
will adhere to critical airfoil surfaces during airplane ground
operations in atmospheric icing conditions.
As discussed later, we propose to revise appendix C of part 25 to
define atmospheric icing conditions specifically for the takeoff phase
of flight. These proposed atmospheric icing conditions would apply
throughout the takeoff path, but are based on the more critical
conditions that would be expected to occur at the end of the takeoff
path. These conditions do not include freezing precipitation on the
ground. At earlier points in the takeoff path, while the airplane is
closer to the ground, the proposed takeoff icing conditions would be
conservative, that is, they would predict larger ice accretions than
would be likely to occur. If these conditions were to actually occur at
ground level, they would form a freezing fog condition that would
probably reduce visibility to the point that takeoffs could not be
made.
An important part of determining the effects of ice accretion on
takeoff performance is to decide at what point in the takeoff ice
accretion is considered to begin. For the purposes of this rulemaking,
we consider ice accretion to begin when the airplane lifts off the
runway surface during takeoff.
Proposed Sec. 25.105(a) would require applicants to determine
airplane takeoff performance for icing conditions if the ice that can
accrete during takeoff results in increasing the reference stall speed
(VSR) or degrading climb performance beyond specified limits. Section
25.105(a) references all regulations related to the takeoff path. As a
result, the performance for the entire takeoff path, including takeoff
speeds and distances, must be determined for icing conditions if the
stall speed or climb performance degradation limits are exceeded.
Section 25.105(a)(2)(i) of the proposal would require applicants to
determine takeoff path performance for icing conditions if the stall
speed increases by more than 3 knots in calibrated airspeed or 3
percent due to ice accretions. This proposed requirement would be more
stringent than the guidance used by the JAA in their draft AMJ 25.1419.
The draft AMJ allowed up to a 5 knot or 5 percent increase in stall
speed before the takeoff performance would need to be recomputed for
icing conditions.
Several commenters on the AMJ, including us, expressed concern over
allowing such a large increase in stall speed believing it would result
in a significant reduction in safety margin between the minimum
operating speeds and the stall speed. We agree with the FTHWG
recommendation that a 3 knot or 3 percent increase in stall speeds is
the maximum that should be permitted before the takeoff performance
data should be recalculated to consider the effects of icing.
Also, the JAA's draft AMJ 25.1419 used the effect of ice accretions
on airplane drag rather than on climb performance to determine when the
takeoff performance data must be provided for icing conditions.
However, we agree with the FTHWG recommendation to consider the effect
[[Page 67283]]
of ice accretions in terms of climb performance in Sec.
25.105(a)(2)(ii) because it would cover more operating variables than
just the effect of ice on airplane drag.
The part 25 takeoff climb requirements include a safety margin by
requiring applicants to determine a net flight path based on the
airplane's actual climb performance capability reduced by a set value
that depends on the number of engines on the airplane. Proposed Sec.
25.105(a)(2)(ii) would require applicants to determine takeoff path
performance specifically for icing conditions if more than half of this
safety margin would be lost due to the effects of ice accretion.
Part 25 divides the takeoff climb performance requirements into
several segments. To establish the allowable limit for takeoff climb
performance degradation in icing conditions, Sec. 25.105(a)(2)(ii)
would consider the effect of ice accretions on just the takeoff climb
segment defined by Sec. 25.121(b). For most transport category
airplanes, this segment most often limits the allowable takeoff weight,
and therefore is the most critical to safety. If the effects of ice
accretions during the takeoff climb segment defined in Sec. 25.121(b)
are beyond specified limits, the airplane performance for the entire
takeoff path must be determined with ice accretions on the airplane.
This would include from the beginning of the takeoff roll until the
airplane is at least 1,500 feet above the takeoff surface. Thus, for
airplanes that would be most affected by ice accretions during the
takeoff climb, additional safety margins would also be provided for the
takeoff ground run even though ice accretion is assumed not to begin
until liftoff.
D. Takeoff Speeds (Sec. 25.107)
We propose to revise Sec. 25.107(c)(3) and (g) to change the
reference for maneuver capability considerations from Sec. 25.143(g)
to Sec. 25.143(h). This is an editorial change due to the
redesignation of Sec. 25.143(g) to Sec. 25.143(h) proposed below.
We also propose to revise Sec. 25.107 by adding a new paragraph
(h). This new paragraph would state that the minimum control speeds
(VMCG and VMC) and minimum unstick speeds
(VMU) determined for the airplane in non-icing conditions
may also be used for the airplane in icing conditions. The
VMU, VMCG, and VMC speeds are used to
determine the takeoff speeds V1, VR, and
V2.
The minimum unstick speed (VMU) is defined in Sec.
25.107(d) as the airspeed at and above which the airplane can safely
lift off the ground and continue the takeoff. Takeoff speeds must be
established sufficiently above this speed to assure the airplane can
safely take off considering the variations in procedures and conditions
that can reasonably be expected in day-to-day operations. Because these
proposals assume that ice accretion does not begin until liftoff, this
proposal would allow the VMU speeds for non-icing conditions
to be used for determining takeoff speeds in icing conditions.
The ground minimum control speed (VMCG) is used in
determining the takeoff V1 speed. The takeoff V1
speed is the highest speed at which the pilot must take the first
action to be able to safely stop the airplane during a rejected takeoff
and the lowest speed at which the takeoff can be safely continued after
an engine failure. Since VMCG, like VMU, occurs
before the airplane lifts off the runway, the assumption is that ice
has not yet begun accreting on the airplane. Therefore, this proposal
would allow the VMCG speeds determined for non-icing
conditions to be used for determining V1 for icing
conditions.
The air minimum control speed, VMC (commonly referred to
as VMCA), is defined in Sec. 25.149(b) as the airspeed at
which it is possible to maintain control of the airplane, with no more
than 5 degrees of bank, when the critical engine is suddenly made
inoperative. Section 25.107 requires the rotation speed (VR)
and the takeoff safety speed (V2) to be sufficiently higher
than VMCA to assure that the airplane will be safely
controllable if the critical engine fails during the takeoff. Since
VR occurs before liftoff, like VMU and
VMCG, this proposal would allow the VMCA speeds
determined for non-icing conditions to be used for determining
VR for icing conditions.
Several concerns must be addressed if we are to allow
VMCA speeds determined in non-icing conditions to be used to
determine V2 in icing conditions. Unlike VR,
V2 occurs after liftoff and ice could have begun accreting
on the airplane. Ice may accrete at V2 because ice
protection systems are typically not turned on until the airplane
climbs more than 400 feet after takeoff. Also, many airplanes do not
have any ice protection on the vertical stabilizer. These concerns
could lead to a reduction in the airplane's directional control
capability if ice accretion occurs. To alleviate these concerns, the
proposed Sec. 25.143(c) would require applicants to show that
airplanes are safely controllable and maneuverable at the minimum
V2 speed with the critical engine inoperative and with the
ice accretion applicable to the takeoff flight phase.
E. Takeoff Path (Sec. 25.111)
Currently, Sec. 25.111 defines the takeoff path, describes the
airplane configuration that applies to each portion of the takeoff
path, and provides airplane performance requirements that must be met.
We propose to revise Sec. 25.111 by adding a new paragraph (c)(5)
stating that the airplane's drag used to determine the takeoff path
after liftoff would be based on the ice accretions defined in the
proposed revision to appendix C. To accommodate the addition of the new
paragraph, the ``and'' at the end of Sec. 25.111(c)(3) would be moved
to the end of Sec. 25.111(c)(4).
The takeoff path begins at the start of the takeoff roll and ends
when the airplane is either 1,500 feet above the takeoff surface, or at
the altitude at which the transition from the takeoff to the en route
configuration is completed and the final takeoff speed attained,
whichever is higher. The takeoff path typically has two distinct climb
segments: One from the point at which the airplane is 35 feet above the
runway up to 400 feet, and the other from a height of 400 feet to the
end of the takeoff path. The proposed changes to Sec. 25.111 would
identify when the takeoff path must be determined for flight in icing
conditions and specify the ice accretion that must be used for these
two climb segments.
New paragraph (c)(5) would refer back to the proposed Sec.
25.105(a)(2) to identify when the takeoff path must be determined for
flight in icing conditions. The ice accretions referenced in new
paragraph (c)(5) would apply to the airborne portions of the takeoff
path, since we are assuming that ice accretion does not begin until
liftoff. If takeoff path performance must be determined for icing
conditions, then the takeoff path must use the takeoff speeds of the
proposed Sec. 25.107 for icing conditions, using the ice accretions
specified in paragraph (c)(5).
F. Landing Climb: All-Engines-Operating (Sec. 25.119)
We propose to revise Sec. 25.119 by requiring the airplane landing
climb performance to be determined for both non-icing and icing
conditions; adding references to the appropriate paragraphs of the
proposed Sec. 25.125 revision for the landing climb speed to use for
non-icing and icing conditions; referring to the proposed appendix C
revision to identify the ice accretion that would be used in
determining landing climb performance in icing conditions; and changing
the speed used to show
[[Page 67284]]
compliance with Sec. 25.119 from a speed less than or equal to
VREF to VREF.
We consider the approach and landing phases of flight to be the
flight phases most affected by icing conditions because of the
potential for descending into and holding in icing conditions prior to
landing. In addition, service history has shown that the majority of
icing accidents and incidents occur in the holding, approach, and
landing flight phases. For these reasons, our policy for the last 40
years has been for applicants to account for the effects of airframe
ice accretion in their airplane's approach and landing climb
performance data provided in the Airplane Flight Manual. (Approach and
landing climb performance refer to the airplane's climb capability in
the approach and landing configurations during the approach and landing
flight phases. Sections 25.121(d) and 25.119 require minimum level of
approach and landing climb performance to ensure that airplanes can
abort an approach or landing attempt and safely climb away.) The
proposed changes to Sec. Sec. 25.119 and 25.121(d) (see below) serve
to codify this policy.
G. Climb: One-Engine-Inoperative (Sec. 25.121)
We propose to revise Sec. 25.121 by rearranging paragraphs (b),
(c), and (d) to specify when the required climb performance must be
determined for icing conditions; refer to the proposed appendix C
revision to identify the ice accretion that would be used in
calculating approach climb performance in icing conditions; and provide
the conditions under which the approach climb speed must be increased
to account for the effect of ice accretion.
Sections 25.121(b) and (c) provide the climb performance
requirements for the takeoff path segments beginning at the point the
landing gear is fully retracted and ending at the end of the takeoff
path. As in the proposed revision to Sec. 25.105, we propose to revise
Sec. 25.121(b) and (c) to require takeoff climb performance to be
determined for icing conditions if the effect of ice: (1) Increases the
stall speed at maximum takeoff weight by more than 3 knots or 3
percent, or (2) reduces the climb performance determined in Sec.
25.121(b) by more than half the safety margin provided by the net
gradient adjustment required by Sec. 25.115.
Section 25.121(a) provides the climb performance requirements for
the takeoff path segment beginning at liftoff and ending when the
landing gear is fully retracted. Since we are assuming that ice
accretion does not begin until liftoff, only a minimal amount of ice
could be accreted during this climb segment. Therefore, the proposal
for Sec. 25.21(g)(1) excludes compliance with Sec. 25.121(a) with ice
accretions on the airplane.
We propose revising Sec. 25.121(d) to state when the approach
climb speed must be adjusted for use in icing conditions. Unlike the
speeds used in the takeoff path, the need to adjust the approach climb
speed would not be based on the effect of ice accretions on the
airplane's stall speed. Instead, the measure for determining whether
the approach climb speed needs to be adjusted for icing conditions is
based on the effect of ice accretions on the approach climb speed. If
the approach climb speed for icing conditions does not exceed the climb
speed for non-icing conditions by more than the greater of 3 knots
calibrated airspeed (CAS) or 3 percent VSR, then non-icing
speeds may be used for calculating approach climb performance for icing
conditions.
The existing requirement for determining the approach climb speed
in non-icing conditions provides applicants some flexibility by only
specifying the maximum allowable approach climb speed. No lower limit
is specified and we have accepted approach climb speeds as low as 1.13
VSR (that is, 13 percent above the reference stall speeds).
We would accept this same level of flexibility for establishing the
approach climb speeds in icing conditions. The approach climb speeds
for icing conditions should also be evaluated to ensure that they
provide adequate maneuver capability.
This proposal for the approach climb segment is less stringent than
the 3 knots or 3 percent VSR standard used for takeoff path
speeds. For example, if the approach climb speed is 1.25 VSR
and VSR is 100 knots, 3 percent of the approach climb speed
is 3.75 knots, while 3 percent of VSR would be only 3 knots.
The approach climb speed could increase by 3.75 knots without requiring
this increased approach climb speed to be used for calculating the
approach climb performance in icing conditions. We consider this small
alleviation to be acceptable since it is only relative to the need for
increasing the approach climb speed for icing conditions. The approach
climb performance must be recalculated with the holding ice accretion
and presented in the AFM regardless of whether the approach climb speed
is adjusted for operations in icing conditions.
H. En Route Flight Paths (Sec. 25.123)
We propose to revise Sec. 25.123(a) by specifying a minimum
allowable speed for determining en route flight paths, which would
apply to both icing and non-icing conditions. The proposed speed,
VFTO, is currently used as the minimum allowable speed for
the final takeoff.
Additionally, the proposed revision to Sec. 25.123(b) would state
when an applicant must determine the en route flight paths specifically
for icing conditions. Similar to the takeoff path requirements of the
proposed revision to Sec. 25.111, en route flight path performance
needs to be specifically determined for icing conditions if the effect
of ice: (1) Increases the en route speed by more than 3 knots or 3
percent, or (2) reduces climb performance by more than half the safety
margin provided by the net gradient adjustment required by Sec.
25.123(b). The ice accretion to be used would be specified in the
proposed revision to appendix C.
The reason for proposing to limit the minimum allowable en route
climb speed to VFTO to is to prevent applicants from showing
compliance with Sec. 25.123 by trading altitude for airspeed when
transitioning from the final takeoff to the en route climb segment.
This clarifying change is consistent with our original intent for Sec.
25.123(a).
Another reason for not allowing an en route climb speed less than
VFTO is that VFTO is the speed at which the
maneuver capability requirements contained in the existing Sec.
25.143(g) must be met in the en route configuration. Allowing an en
route climb speed lower than VFTO would not ensure that the
airplane has adequate maneuvering capability during the en route climb
phase of flight.
We are not proposing any changes to the two-engine-inoperative en
route flight path requirements contained in Sec. 25.123(c) for flight
in icing conditions. We do not expect the pilot to stay in icing
conditions with one engine inoperative for a long enough duration for
the failure of a second engine in icing conditions to be an issue.
En route and takeoff flight paths have similar safety issues.
Therefore, we are proposing requirements for identifying when en route
climb flight paths must be determined for icing conditions that are
similar to those proposed for takeoff flight paths. The only
significant difference is that for the en route climb paths, a speed of
1.18 VSR determined with the en route ice accretion of
proposed appendix C is compared to the en route climb speed selected
for non-icing conditions instead of comparing stall speeds with and
without ice accretions.
The reason for this difference is to provide a more stringent
requirement
[[Page 67285]]
for airplanes that use the minimum allowable en route climb speed of
1.18 VSR. (1.18 VSR is the minimum allowable
value of VFTO prescribed by Sec. 25.107(g)). Airplanes that
use a higher en route climb speed have a larger speed margin to the
stall speed and more maneuvering capability in the en route climb phase
to help offset the negative effects of ice accumulation.
Due to differences in their methods of generating thrust,
propeller-driven airplanes generally have better climb performance at
lower airspeeds than turbojet-powered airplanes. To optimize
performance, the en route climb speed used for propeller-driven
airplanes is usually the minimum allowable speed of 1.18
VSR, while the en route climb speed used for turbojet-
powered airplanes is usually higher. Therefore, the proposed
requirement would be more stringent for propeller-driven airplanes. We
consider the increased stringency for propeller-driven airplanes to be
desirable for the following reasons:
Propeller-driven airplanes generally have deicing systems
that cycle on and off, allowing ice to accrete on the protected
surfaces before removing it. Also, these deicing systems typically do
not remove all of the ice with each cycle, leaving some residual ice.
Both of these effects result in drag increases that are generally not
present on turbojet airplanes that have ice protection systems using
hot bleed air from the engines.
Propeller-driven airplanes will likely be subjected to
increased exposure to icing conditions, due to their slower operating
speeds, shorter flight lengths, and lower cruising altitudes.
I. Landing (Sec. 25.125)
We propose to revise Sec. 25.125(a) to identify when the landing
distance must be determined specifically for icing conditions. The
proposed requirement would specify that the landing distance must be
determined for icing conditions if the VREF in icing
conditions exceeds the VREF in non-icing conditions by more
than 5 knots CAS. For icing conditions, the landing distance would be
determined with the landing ice accretion defined in the proposed
revision to appendix C.
Additionally, a new paragraph (b) would be added to include the
landing distance requirements that would be moved from the existing
paragraph (a). The new paragraph (b) would also set the requirements
for determining the landing speeds to use in determining the landing
distances for both icing and non-icing conditions. For icing
conditions, the landing speed must not be lower than 1.23
VSR0 with the landing ice accretion on the airplane if that
speed exceeds the VREF for non-icing conditions by more than
5 knots CAS.
The existing paragraphs (b) through (f) would be redesignated as
(c) through (g).
Whether landing distances or landing speeds must be determined
specifically for icing conditions depends on whether VREF
needs to be increased by more than 5 knots CAS to counteract the effect
of ice on airplane stall speeds. The reasons behind allowing
VREF to increase by up to 5 knots CAS in icing conditions
before requiring landing distance performance to be recomputed for
icing conditions are:
As part of the flight testing to demonstrate compliance
with the landing distance requirements, we typically evaluate airplane
controllability when landing at speeds lower than the normal landing
speeds. We usually perform this evaluation at a speed 5 knots below
VREF to cover inadvertent speed variations that may occur in
operational service. Plus or minus five knots variation from
VREF is frequently used as a guideline for evaluating
expected operational variations in landing speeds.
Normal approaches in transport category airplanes are
typically flown at speeds above VREF to provide speed
margins to account for wind gusts. Although the additional speed should
be bled off by the time that the airplane is over the landing
threshold, it may not be. Service history does not indicate any safety
problems with the resulting longer landing distance.
Many transport category airplanes are flown at a speed 5
knots higher than VREF during final approach to counter any
inadvertent speed loss. Often this additional speed has not been bled
off before reaching the landing threshold. Again, service history does
not indicate any safety problems with the resulting longer landing
distance.
A 5-knot increase above the VREF speed for non-
icing conditions equates to approximately 3 percent of the 1-g stall
speed (slightly less than 3 percent for larger airplanes). This is
consistent with the allowable stall speed increase proposed for the
takeoff path requirements for icing conditions.
As a further safety consideration for the VREF speed,
Sec. 25.125(b)(ii)(c) would require that VREF for icing
conditions must provide the same maneuvering capability (with ice
accretions on the airplane) as is currently required at VREF
for non-icing conditions. This may result in an increase to
VREF for icing conditions even if this increase is less than
5 knots.
The current Sec. 25.125(a)(2), which would be redesignated as
Sec. 25.125(b)(2)(i), requires VREF for non-icing
conditions to be not less than the landing minimum control speed,
VMCL. This existing requirement ensures that adequate
directional control is available in case an engine fails during a go-
around. Under the proposed new rule, the VMCL determined for
non-icing conditions would continue to be used for icing conditions.
This would be similar to the takeoff flight phase, where the takeoff
minimum control speeds, VMCG and VMCA, determined
for non-icing conditions would continue to be used for icing
conditions. Unlike the takeoff case; however, the continued use of the
non-icing VMCL is not explicitly stated. We consider the
proposed requirements to adequately address this issue without
proposing an additional explicit requirement. Section 25.125(b)(2)(ii)
requires VREF for icing conditions to be not less than
VREF for non-icing conditions. Under Sec. 25.125(b)(2)(i),
VREF for non-icing conditions must be not less than
VMCL for non-icing conditions. Taken together, these two
proposed requirements would allow the VMCL determined for
non-icing conditions to continue to be used for icing conditions.
To assure that using the VMCL determined for non-icing
conditions will provide safe controllability and maneuverability for
icing conditions, the proposed Sec. Sec. 25.143(c)(2) and (c)(3) would
require the applicant to show that the airplane will be safely
controllable and maneuverable during an approach and go-around and an
approach and landing, both with the critical engine inoperative. For
added safety during certification flight testing, these maneuvers may
be accomplished with a simulated engine failure (as noted in the
proposed advisory material associated with this proposal).
J. Controllability and Maneuverability--General (Sec. 25.143)
We propose to revise Sec. 25.143 to add a new paragraph (c) that
requires the applicant to show that the airplane with ice accretions
and with the critical engine inoperative is safely controllable and
maneuverable during takeoff, an approach and go-around, and an approach
and landing; a new paragraph (i) to identify the ice accretions that
must be used in showing compliance with Sec. 25.143 in icing
conditions, and to introduce two specific controllability requirements
that apply to flight in icing conditions; and a new paragraph (j) to
specify tests for ensuring that the airplane has adequate
controllability for flight in icing conditions before the ice
[[Page 67286]]
protection system is activated and performing its intended function of
removing any ice accretions from protected surfaces.
In addition, existing paragraphs (c) through (g) would be
redesignated as paragraphs (d) through (h), and paragraph references in
the newly designated paragraphs (d), (e), and (f) would be revised
accordingly.
The requirements proposed in new paragraph (c) are intended to
ensure that using the minimum control speeds for non-icing conditions
would not result in controllability and maneuverability safety concerns
when the same speeds are used for icing conditions.
The proposed new paragraph (i)(1) would require compliance with all
of Sec. 25.143 in icing conditions except paragraphs (b)(1) and (2).
Sections 25.143(b)(1) and (2) are excepted from icing analysis under
proposed section 25.21(g).
These proposed requirements assume a conventional empennage (that
is, wing/fuselage/tailplane) configuration. Special conditions, issued
in accordance with Sec. 21.16, may be necessary for certification of
airplanes with an unconventional empennage configuration.
Applicants can minimize the number of ice accretions to be tested
by using one accretion that is shown to be the most critical accretion
for several flight phases.
In many cases, a thin, rough, layer of ice (defined as sandpaper
ice in the proposed revision to appendix C) has been shown to have a
more detrimental effect on handling qualities for airplanes with
unpowered control systems than larger ice accretions. The effect of
sandpaper ice accretions may be more significant than larger ice
accretions on these airplanes. In some cases, such an accretion has
resulted in control surface hinge moment reversals that required the
flightcrew to apply extremely high forces to the controls to regain
control of the airplane. Applicants would have to consider sandpaper
ice in showing compliance with the proposed Sec. 25.143(i).
The proposed paragraph (i)(2) would require applicants to conduct a
pushover maneuver down to a zero g load factor with the critical ice
accretion on the airplane. (If the airplane lacks enough elevator power
to get to a zero g load factor, the maneuver may be ended at the lowest
load factor obtainable.) The purpose of this proposed requirement is to
evaluate an airplane's susceptibility to a phenomenon known as ice-
contaminated tailplane stall (ICTS). Ice-contaminated tailplane stall
can be characterized either by completely stalled airflow over the
horizontal stabilizer, or by an elevator hinge moment reversal due to
separated flow on the lower surface of the horizontal stabilizer caused
by ice accretions on the tailplane.
Several incidents and accidents have been caused by ICTS. These
incidents and accidents have typically occurred during landing approach
when the flightcrew either lowered the flaps or abruptly decreased the
airplane's pitch attitude. Either of these actions will increase the
angle-of-attack (AOA) of the local airflow over the tailplane. If there
is ice on the tailplane, the increased AOA may lead to an ICTS.
The proposed pushover maneuver increases the AOA on an ice-
contaminated tailplane by inducing a nose down pitch rate. An airplane
is not susceptible to an ICTS if, during the pushover maneuver:
The pilot must continue to apply a push force to the pitch
control throughout the maneuver (that is, the airplane will not
continue the maneuver to or toward a zero g load factor unless the
pilot applies a push force to the pitch control); and
The pilot can promptly recover from the maneuver without
exceeding 50 pounds of pull force on the pitch control.
The proposed pushover maneuver evolved from earlier criteria
developed shortly after a series of incidents and accidents highlighted
the safety concerns related to ICTS. For example, early ICTS test
criteria called for executing a pushover to a 0.3 g to 0.4 g load
factor with a pitch rate of not less than 10 degrees per second in an
attempt to copy the documented ICTS accident conditions. An aggressive
pushover to zero g was later found to result in the same combination of
load factor and pitch rate, but with the advantage of not needing
sophisticated test instrumentation to perform the test.
In addition to the pushover maneuver, we propose that applicants
demonstrate the safety of a sideslip maneuver with an ice-contaminated
tailplane, since this has been shown to be a more critical ICTS
triggering maneuver for some airplanes. The proposed Sec. 25.143(i)(3)
would require that any changes in the force the pilot must apply to the
pitch control to maintain speed with increasing sideslip angle must
steadily increase with no force reversals.
Proposed Sec. 25.143(j) would address airplane controllability
between the time when the airplane first enters icing conditions and
when the ice protection system is activated and performing its intended
function. In developing the controllability criteria proposed in
paragraph (j), we considered the likely duration of this time period
and the means that might be used for detecting icing conditions and
activating the ice protection system. The proposed advisory material
for part 25, appendix C, part II(e) would provide additional guidance
for determining the appropriate ice accretion for this testing based on
the means of ice detection.
Although activation of the ice protection system is expected to
occur shortly after entering icing conditions, it may not occur for a
relatively long time if the method of detecting icing conditions
depends on the crew visually observing a specified amount of ice
buildup on some reference surface (for example, windshield wiper, icing
probe). To address this concern, proposed Sec. 25.143(j)(1) requires
compliance with all of the requirements of Sec. 25.143 that would
apply to flight in icing conditions for this method of detecting icing
conditions. In this case, the ice accretion to be used in showing
compliance would be the ice accretion that would exist before the ice
protection system is activated and is performing its intended function.
For airplanes that use other means of detecting icing conditions,
the proposed requirements would be less stringent. This reflects the
expectation that the airplane would fly only briefly in icing
conditions before activation of the ice protection system. Instead of
requiring compliance with all of the requirements of Sec. 25.143 that
apply to flight in icing conditions, Sec. 25.143(j)(2) would require
only a demonstration that the airplane is controllable in a pull-up
maneuver up to 1.5 g load factor, and that there is no longitudinal
control force reversal during a pushover maneuver down to a 0.5 g load
factor.
K. Stall Warning (Sec. 25.207)
We propose to revise paragraph (b) to require that the means for
providing a warning of an impending stall must be the same for both
icing and non-icing conditions. There would be one exception to this
general rule. If the means of detecting icing conditions does not
involve waiting until some specified amount of ice has accreted on a
reference surface, then the stall warning may be provided by a
different means during the time from when the airplane first enters
icing conditions until the ice protection system is activated and is
performing its intended function.
We propose to add a new paragraph (e) to specify the stall warning
margin that the stall warning system must provide in icing conditions.
The stall
[[Page 67287]]
warning margin is how far in advance the pilot is warned of a potential
stall. We propose to evaluate the stall warning margin in both straight
and turning flight while decelerating the airplane at rates of up to
one knot per second. The pilot must be able to prevent stalling the
airplane using the same recovery maneuver that would be used in non-
icing conditions, starting the recovery maneuver not less than 3
seconds after the stall warning begins. Paragraph (e) also specifies
the ice accretions that would be used for showing compliance.
We propose to revise paragraph (f) to consist of the existing
paragraph (e), revised to clarify that the pilot must use the same
maneuver to demonstrate that the airplane can safely recover from a
stall in icing conditions as is used for non-icing conditions.
We propose to add a new paragraph (h) to specify the stall warning
requirements for the time period when the airplane first enters icing
conditions until the ice protection system is activated and is
performing its intended function. The proposed stall warning
requirements would be different for different means of detecting icing
conditions and whether or not the stall warning is provided by the same
means for icing conditions and non-icing conditions.
Currently, part 25 requires airplanes to provide the flightcrew an
adequate warning of an impending stall so that the flightcrew can
prevent the stall. The current requirement does not consider the
effects of ice accretions on the airplane. With ice accretions on the
airplane, the airplane may stall sooner (that is, at a higher speed or
lower AOA), possibly even before the stall warning would occur. For an
airplane to be approved for flight in icing conditions, we consider it
necessary to provide an adequate stall warning margin with ice
accretions on the airplane. For human factors reasons, we also consider
it necessary for the means of providing the stall warning to be the
same in icing conditions and non-icing conditions. But as discussed in
the specific proposal for Sec. 25.207(h), we would allow a limited
exception to this general requirement.
In most transport category airplanes, the stall warning is provided
by a device called a stick shaker, which shakes the control column to
alert the pilot when the airplane is close to stalling. The proposed
addition to Sec. 25.207(b) would establish the general requirement for
the same means for the stall warning in icing conditions and non-icing
conditions. Section 25.207(b) would, however, allow an exception to the
general requirement. The conditions for the exception to the general
requirement would be established in Sec. 25.207(h)(2)(ii).
The general rule of Sec. 25.207(b) may result in a different stick
shaker activation point for icing conditions because the airplane may
stall at a different speed or AOA with ice accretions. In order to
maintain a safe margin above the stall speed and to provide sufficient
maneuvering capability, an increase in the minimum operating speeds may
be needed. Increasing the minimum operating speeds, such as takeoff and
landing speeds, may result in a cost increase if operators have to
reduce payload to comply with performance requirements at the higher
operating speeds.
These potential cost impacts may be minimized for stall warning in
icing conditions after the ice protection system has been turned on.
Then the higher settings for flight in icing conditions would only be
used if the ice protection system has been activated. The higher
operating speeds would not be a factor, or cost, in other operations.
However, this design solution would not protect the airplane during
the time that the airplane is in icing conditions before activation of
the ice protection system. To protect the airplane during this time
period, any changes to the stall warning system settings for potential
ice accretions would need to be active at all times. This would mean
that the minimum operating speeds would be increased for both icing and
non-icing conditions with resulting cost implications.
To minimize the potential cost impact, while ensuring flight
safety, the FTHWG examined whether different stall warning requirements
could be used for flight in icing conditions before activation of the
ice protection system. Flight in icing conditions before activation of
the ice protection system is a temporary condition. In most cases, this
time is expected to be relatively short. In those cases, proposed
paragraph (h)(2) would allow the stall warning to be provided by a
different means than is used for non-icing conditions. For example,
natural airplane buffeting might be used instead of a stick shaker. By
allowing a different means of stall warning, the need to change the
stall warning system setting would be minimized.
However, if the stall warning is provided by a different means than
for flight in non-icing conditions, the proposal seeks to balance this
with more stringent flight demonstration requirements. The requirements
would be more stringent for demonstrating that the pilot can safely
recover the airplane after a stall warning has occurred. This
demonstration occurs during the flight tests to show acceptable flight
characteristics for stall recovery. For the time that the airplane is
in icing conditions before the ice protections system has been
activated, if stall warning is provided by a different means than for
non-icing conditions, it may take longer for the flightcrew to
recognize the impending stall and take recovery action. Therefore,
instead of allowing a recovery maneuver to be started one second after
the onset of stall warning, the recovery maneuver must not begin until
at least 3 seconds after the onset of stall warning. Paragraph
(h)(2)(i) of the proposal allows the recovery to start within one
second of the stall warning. The more stringent three-second
requirement is contained in the proposed paragraph (h)(2)(ii).
Additionally, proposed paragraph (h)(2)(ii) would require the
applicant to show that the airplane has safe handling qualities in case
the flightcrew does not take suitable recovery action in time to
prevent stalling. Compliance with the stall characteristics
requirements of Sec. 25.203 would be required for stalls demonstrated
using a one knot per second deceleration rate.
Earlier, we stated that in most cases, flight in icing conditions
before activation of the icing system is expected to be relatively
brief. However, if the means of detecting icing conditions and
activating the ice protection system depends on the flightcrew visually
identifying a discrete amount of ice on a reference surface (for
example, one-quarter-inch of ice on the wing's leading edge), then this
temporary condition may be of a relatively long duration. Therefore, we
consider it appropriate to apply the same requirements for stall
warning to this case as are applied to the case of flight in icing
conditions after the ice protection system is fully active. For this
case, we propose that the stall warning indication must be provided by
the same means as in non-icing conditions. Proposed paragraph (h)(1)
contains this requirement.
The FTHWG determined that applying the existing stall warning
margin requirements of Sec. 25.207(c) and (d) to icing conditions
would be far more stringent than best current practices and would
unduly penalize designs that have not exhibited safety problems in
icing conditions. The FTHWG examined whether the stall warning
requirements of existing Sec. 25.207(c) and (d) could be made less
stringent for icing conditions without
[[Page 67288]]
compromising safety. The proposed Sec. 25.207(e) resulted from this
effort.
In developing the proposed Sec. 25.207(e), the FTHWG determined
that the types of transport category airplanes involved in icing-
related stall accidents:
Were equipped with deicing boots that operated cyclically
(for example, a boot cycle every one to three minutes), and
Were generally very susceptible to large affects on stall
speeds from ice accretions during the periods between boot cycles
(known as intercycle ice).
The proposed criteria of Sec. 25.207(e), in combination with the
proposed Sec. 25.207(b), would likely require different stall warning
system settings for icing conditions and non-icing conditions on future
airplanes with those characteristics. These proposals would have a
lesser impact on airplanes without those characteristics. The stall
warning settings established for the airplane without ice accretions
may be retained for operation in icing conditions, provided they are
still adequate to prevent stalling if the pilot does not take any
action to recover until three seconds after the initiation of stall
warning. Since all modern conventional transport category airplanes use
some type of artificial stall warning system (stick shaker or combined
aural and visual warning), and since three seconds is considered
adequate time for response by a trained pilot, we agree with the FTHWG
that this stall warning definition would be acceptable for icing
conditions.
The proposed revision of Sec. 25.207(f) would require the pilot to
use the same stall recovery maneuver during the compliance
demonstration for icing conditions as is used for non-icing conditions.
This proposal is based on human factors considerations. In operational
service, pilots would not be expected to respond differently to a stall
warning indication in icing conditions versus non-icing conditions.
L. Wind Velocities (Sec. 25.237)
The proposed revisions to Sec. 25.237(a) would add a requirement
to establish a safe landing crosswind component for use in icing
conditions. The proposed revision to paragraph (a) also would state
that the crosswind component established for takeoff without ice
accretions may be used for takeoffs conducted in icing conditions.
For taking off in crosswinds, we consider it unnecessary to
consider the effect of ice accretions since these proposals assume that
ice accretions do not begin until liftoff. Therefore, airplanes will
accrete very little ice, if any, while close to the ground where
crosswinds are a significant safety concern. Proposed Sec.
25.237(a)(2) explicitly states that the takeoff crosswind component
without icing is valid for icing conditions.
However, the conditions on landing are different. Before landing,
the airplane may spend a significant amount of time exposed to icing
conditions. These ice accretions may affect directional control when
crosswinds are encountered close to the ground. As a result, (a)(3)(ii)
requires evaluation of the landing crosswind component with ice
accretion.
M. High-Speed Characteristics (Sec. 25.253)
We propose to revise Sec. 25.253 by adding a new paragraph (c) to
define the maximum speed for stability characteristics, VFC/
MFC, for icing conditions. The proposal would permit
applicants to define a VFC/MFC for icing
conditions that is different than the VFC/MFC
defined for non-icing conditions. Additionally, Sec. 25.253(b) would
be revised to refer to Sec. 25.143(g) rather than Sec. 25.143(f) due
to the proposed renumbering of Sec. 25.143.
VFC/MFC is the highest speed at which
compliance with several airplane handling qualities requirements must
be shown. The FTHWG's review of historical certification data showed
that none of the flight tests for airplane handling qualities performed
with ice accretions were conducted above 300 knots CAS. The air loads
associated with such high speeds tend to make it difficult to keep
either artificial or natural ice attached to the airframe to accomplish
the testing. It also minimizes the possibility of encountering this
condition in operational service. Therefore, we propose that the
maximum speed for demonstrating stability characteristics with ice
accretions is the lower of VFC, 300 KCAS, or any other speed
at which it can be shown that the airframe will be free of ice.
N. Pilot Compartment View (Sec. 25.773)
We propose to revise Sec. 25.773(b)(1)(ii) to replace the phrase
``if certification with ice protection provisions is requested'' with
``if certification for flight in icing conditions is requested.''
The proposed change is necessary to be consistent with the proposed
change to Sec. 25.1419. As discussed in the reason for revising Sec.
25.1419, compliance with icing-related safety of flight requirements
should depend on whether the airplane would be approved to operate in
icing conditions, not on whether the airplane has approved ice
protection provisions installed.
O. Inlet, Engine, and Exhaust Compatibility (Sec. 25.941)
We propose to revise the references to Sec. Sec. 25.143(c), (d),
and (e), contained in paragraph (c) of Sec. 25.941, to read Sec.
25.143(d), (e), and (f).
The proposed changes are necessary to maintain references to the
correct paragraphs of Sec. 25.143 if the changes to Sec. 25.143 being
proposed by this rulemaking are adopted.
P. Ice Protection (Sec. 25.1419)
We propose to revise the introductory text of Sec. 25.1419 to
replace the phrase, ``If certification with ice protection provisions
is desired * * *'' with ``If certification for flight in icing
conditions is desired * * *'' The current rule requires an applicant to
demonstrate an airplane's ability to safely operate in icing conditions
only when the applicant is seeking to certificate ice protection
features. It fails to address certification approval for flight in
icing conditions for airplanes without ice protection features. The
proposed revision, which would adopt the existing wording from JAR
25.1419, would require an applicant to demonstrate the airplane's
ability to safely operate in icing conditions whenever the applicant is
seeking approval for flight in icing conditions.
We also propose to simplify the second sentence of Sec. 25.1419 to
remove redundant wording. This change is editorial in nature and is not
intended to change the requirement in any way.
We propose to amend Sec. 25.1419 to incorporate the revised
introductory text for the following reasons:
A literal reading of the current Sec. 25.1419 wording
could imply that the applicant does not have to demonstrate that the
airplane can be safely operated in icing conditions unless an ice
protection system is installed.
The revised text would clarify that any airplane approved
to fly in icing conditions must be capable of operating in the icing
conditions of appendix C of part 25 regardless of whether or not the
airplane has an ice protection system.
Q. Part 25, Appendix C
We propose to revise appendix C of part 25 to create two
subsections: Part I to define the atmospheric icing conditions that
must be considered when showing compliance with the icing-related
requirements of part 25, and part II to define ice accretions for each
phase of flight. We also propose to add a definition of the atmospheric
icing conditions to use specifically for the takeoff phase of flight.
[[Page 67289]]
Proposed Appendix C, Part I
Proposed appendix C, part I would contain the existing appendix C
definitions of atmospheric icing conditions. We propose adding a
definition of ``takeoff maximum icing,'' which is to be used in
determining ice accretions for the takeoff phase of flight.
Proposed Appendix C, Part II
Proposed appendix C, part II(a) would contain definitions of the
ice accretions appropriate to each phase of flight. Proposed appendix
C, part II(b) would provide options for reducing the number of ice
accretions to be considered for each phase of flight. Proposed appendix
C, part II(c) would permit applicants to use, for the airplane
performance tests, the same ice accretion used for evaluating handling
characteristics. Proposed appendix C, part II(d) would define the
conditions for determining the ice accretions for the takeoff phase of
flight. Proposed appendix C, part II(e) would define what ice accretion
must be considered prior to normal ice protection system operation.
One early concern with developing appropriate airplane performance
and handling qualities requirements for the takeoff phase of flight was
the atmospheric icing environment close to the ground. The FTHWG
members expressed significant concerns with using the existing appendix
C atmospheric icing envelopes for this purpose. The FAA meteorologists
confirmed that the existing appendix C atmospheric envelopes are not
generally representative of icing conditions close to the ground.
In general, for determining the size, shape, location, and texture
of ice accretions on the airplane, one needs information about the
atmospheric icing environment, i.e., icing cloud size, cloud liquid
water content, water droplet size, expressed in terms of the mean
effective diameter of the droplets, and ambient air temperature.
We propose to use the following definition of atmospheric icing
conditions for takeoff maximum icing conditions in appendix C, part
I(e): An icing cloud extending from ground level to a height of 1,500
feet above the takeoff surface with a liquid water content of 0.35
grams/meter 3, water droplets with a mean effective diameter
of 20 microns, and an ambient temperature of minus 9 degrees Celsius (-
9[deg] C). The following discussion presents the reasons for selecting
these values.
Since the takeoff phase of flight is relatively short, generally
ending at a height of 1,500 feet above the takeoff surface (ref. Sec.
25.111(a)), we consider it reasonable to assume that the entire takeoff
phase could be flown within the same icing cloud. Therefore, we propose
that the takeoff maximum icing conditions would extend from ground
level to a height of 1,500 feet above the level of the takeoff surface.
Although measured data for liquid water content at low altitudes
are sparse, a comparison of data contained in the FAA Technical
Center's database on inflight icing conditions with theoretical
predictions suggest a maximum liquid water content within the icing
cloud of 0.35 grams/meter 3 from ground level up to 1,500
feet. We propose to use this value within the definition of the maximum
takeoff icing conditions. This proposed value would also cover the
potential for dense ground fog at freezing temperatures, which our
meteorologists stated would expose the airplane to a liquid water
content of approximately 0.30 grams/meter 3.
For the size of the water droplets, both industry and FAA icing
specialists concurred that a mean effective diameter of 20 microns
would be appropriate for icing conditions occurring near ground level.
We propose to use this value within the definition of the maximum
takeoff icing conditions.
Selection of the ambient temperature for takeoff icing was based on
theoretical predictions that showed the effect of temperature to
decrease significantly as the temperature itself decreased. We propose
to use an ambient temperature for the takeoff icing atmosphere of minus
9 degrees Celsius (-9[deg] C), the point at which any further decrease
in temperature had a negligible effect on the resulting ice accretion.
According to our meteorologists, the amount of water vapor that can
be held without condensing in a given volume of space depends only on
the temperature of the gas (water vapor, air, etc.) in that space. It
does not vary with altitude. Therefore, the proposed takeoff icing
atmosphere would be equally applicable to all airport runway
elevations.
Proposed part II(a) references specific phases of flight and
defines the critical ice accretions associated with the specific phase
of flight. In the main body of the rule, various sections require
evaluation using the ice accretion defined in appendix C. Proposed part
II(a) contains those definitions. For example, Sec. 25.125(a)(1)
requires evaluation of landing distance using the ice accretion defined
in appendix C. To perform the evaluation required by Sec.
25.125(a)(1), an applicant would use the landing ice definition found
in paragraph (5) of this section.
To reduce the number of artificial ice accretions that must be
considered, proposed part II(b) would permit the ice accretion
determined for one flight phase to be used in showing compliance with
the flight requirements of another phase, provided the applicant can
show it has a more critical effect on the flight parameter being
evaluated. For example, using the ice accretion determined for the
holding phase to show compliance with the requirements for the takeoff
phase will generally have a larger effect on performance and therefore
be more penalizing than using an ice accretion determined specifically
for the takeoff phase.
Proposed part II(c) clarifies that the ice accretion with the most
adverse effect on handling qualities may also be used during the flight
test demonstrations of performance as long as any performance
differences are conservatively taken into account. This proposed
section is consistent with the intent behind proposed part II(b) to
reduce the number of ice accretions that must be considered. Unlike
handling qualities, performance effects between relatively small
differences in ice accretion generally can be addressed adequately
through analysis.
Proposed part II(d) states the assumptions under which the takeoff
ice accretions are determined. Proposed part II(d) also states that it
must be assumed that the crew does not take any action to activate the
ice protection system until the airplane is at least 400 feet above the
takeoff surface. This requirement is consistent with the existing
requirement of Sec. 25.111(c)(4) that limits the types of
configuration changes requiring crew action before reaching 400 feet
above the takeoff surface.
We consider it necessary to also take into account the effects of
any ice accretion that may form on the airplane from the time the
airplane enters icing conditions until the ice protection system is
activated and is performing its intended function. The size, shape,
location, and texture of this ice accretion will depend on: (1) The
means used to identify that the airplane is in icing conditions (for
example, the pilot seeing ice accreting on the airplane, an ice
detector, a combination of freezing temperatures and visible moisture),
(2) the means and procedures for activating the ice protection system
(for example, the pilot manually activating the system after a
specified amount of ice builds up or automatic activation), and (3) the
[[Page 67290]]
system characteristics (for example, the time it takes to effectively
remove the ice). We propose to define the ice accretion applicable to
the time period before the ice protection system has been activated and
is performing its intended function as a period of time in the
continuous maximum icing conditions of proposed part I of appendix C,
including:
The time for recognition,
A delay time appropriate to the means of ice detection and
activation of the ice protection system, and
The time needed for the ice protection system to perform
its intended function after manual or automatic activation.
III. Discussion of Non-Consensus Issues
One of the goals of the ARAC process is consensus on the proposed
recommendations. Due to the variety of interests represented in the
FTHWG, this goal was not fully achieved. The areas of non-consensus,
however, were confined to specific details within the proposals, and
not to the overall need to amend part 25 to address airplane
performance and handling qualities in icing conditions. The issues for
which full consensus was not achieved within the FTHWG were:
1. The requirement that a push force must be needed throughout the
pushover maneuver proposed in the new Sec. 25.143(i)(2);
2. Whether the test to evaluate longitudinal handling qualities
during sideslip maneuvers should be required by regulation as proposed
in the new Sec. 25.143(i)(3), or should only be included in advisory
material as one means of showing compliance;
3. Whether the same airplane performance and handling qualities
requirements (Sec. Sec. 25.143(j) and 25.207(h)) should always apply
whenever the means to activate the ice protection system depends on the
pilot to visually identify when the airplane is in icing conditions;
and
4. Whether the proposed revision to appendix C adequately ensures
that the full range of variables are considered in determining what the
critical ice accretion is for a particular flight phase.
Each of these non-consensus issues is discussed in more detail
below.
A. Non-Consensus Issue 1--Sec. 25.143(i)(2)
The FTHWG did not reach a consensus on the issue of requiring a
push force throughout the maneuver down to a zero g load factor (or the
lowest load factor obtainable if limited by elevator power). Although
there was consensus that the test maneuver should be performed to zero
g, the group did not reach a consensus on whether the pilot should be
required to apply a push force to the longitudinal control system
throughout the maneuver until a zero g load factor is attained. The
FTHWG considered two alternatives.
Alternative 1 was developed by FTHWG members who did not support
our proposal of requiring a push force to be maintained down to zero g
load factor in the pushover maneuver. These FTHWG members disagreed
with the proposal for the following reasons:
Historically, the pushover test was performed to a 0.5 g
load factor rather than zero g. For example, as practiced by Transport
Canada (the Canadian airworthiness regulatory authority), this
demonstration was done with a high pitch rate. Consequently, there was
significant overshoot of the 0.5 g load factor, down to approximately
0.25 g or less. This maneuver was intended to be a controllability test
beginning with the pilot abruptly pushing on the control column to
achieve a high nose-down pitch rate, followed by a pull to recover. The
intent was not to reach a specific g level below 0.5 g, but to show
that the pilot could perform a satisfactory recovery. This has proven
to be an acceptable test technique. To date, airplanes evaluated with
this technique have had a satisfactory safety record in service.
Since the beginning of the 1980s, the practice of many
certification authorities has been to require testing to lower load
factors. This evolved until the introduction of the JAA's NPA 25F-219,
which not only requires testing to zero g, but also requires a push
force throughout the maneuver to zero g. A zero-g pushover is
considered to be an improbable condition, going well beyond any
operational maneuver, and does not properly represent gusts, pitch
rate, elevator position, or other factors that may contribute to
tailplane stalls. Also, since the NPA requirement was developed for a
specific turboprop, and motivated by service experience on turboprop
airplanes, other requirements were proposed for other types of
airplanes.
For the above reasons, the supporters of alternative 1 to Sec.
25.143(i)(2) consider that requiring a push force to load factors as
low as zero g is excessive. Instead, they recommend replacing proposed
Sec. 25.143(i)(2) with:
The airplane must be controllable in a pushover maneuver down to
zero g, or the lowest load factor obtainable if limited by elevator
power. It must be shown that a push force is required throughout the
maneuver down to 0.5 g. It must be possible to promptly recover from
the maneuver without exceeding 50 pounds pull control force.
Further supporting rationale: FAA Advisory Circular 25-7A, ``Flight
Test Guide for Certification of Transport Category Airplanes,'' defines
the boundaries of various flight envelopes. With regard to the minimum
load factor with flaps down:
The normal flight envelope (NFE) goes to 0.8 g;
The operational flight envelope (OFE) goes to 0.5 g; and
The limit flight envelope (LFE) goes to zero g.
Conceptually, the boundaries of the OFE are as far as the pilot is
expected to go intentionally, while the LFE is based on structural or
other limits that should not be exceeded. Between the OFE and the LFE,
it is acceptable for degraded handling qualities, but the airplane must
remain controllable and it must be possible to avoid exceeding the
limit load factor (see Sec. 25.143(b)).
Although existing regulations do not allow force reversals (for
example, from a push force on the control column to a pull force in
this case) for the en route flight phase, in practice, the
certification tests for these rules do not cover the full structural
limit flight envelope. Rather, the certification tests cover a
reasonable range of load factors sufficient to cover normal operations.
For example, in the en route configuration, where the limit minimum
load factor is usually negative 1 g, the JAA's Advisory Circular Joint
(ACJ) No. 2 to JAR 25.143(f) states: ``* * * assessment of the
characteristics in the normal flight envelope involving normal
accelerations from 1 g to zero g, will normally be sufficient.''
With flaps up, zero g is the midpoint between the limit load factor
and the trim point. The corresponding points for flaps down are zero g
for the limit load factor and 0.5 g for the midpoint assessment of
characteristics. The supporters of alternative 1 to Sec. 25.143(i)(2)
are concerned that requiring a push force to zero g means that this
limit load factor will be routinely exceeded in the flight tests used
to show compliance with the proposed rule.
The zero-g pushover is not like typical stability tests where it is
possible to establish steady state conditions and measure a repeatable
control force. The pushover is an extremely dynamic maneuver lasting
only a few seconds and involving high pitch rates in both directions.
There will always be variability due to pilot technique. The pilot may
pull slightly before reaching zero g to reduce the nose-down pitch rate
and anticipate the recovery. This
[[Page 67291]]
makes it impossible to distinguish between the force required to reach
a given g level and the force the pilot applies to track the targeted
pitch rate. At critical conditions, airplanes that meet the criterion
suggested in the alternative proposal still require a significant pull
force to recover.
Alternative 1 to Sec. 25.143(i)(2) would set a limit of 50 pounds
on the total control force needed to recover promptly. This would
ensure that the force that the pilot must exert is low enough so that
even with only one hand on the pitch control (the other hand might be
on the thrust levers or another control), the pilot can handle a
combination of:
The force to halt the nose-down pitch rate,
The force due to any hinge moment reversal, and
The force to establish a satisfactory nose-up pitch rate
for recovery.
The 50-pound limit is used for a similar purpose in several other
rules. The effect of data scatter and variations in pilot technique
will cause airplanes that are not clearly free of ICTS concerns to
exceed the 50-pound limit too often, so they will not pass this test.
The supporters of alternative 1 to Sec. 25.143(i)(2) believe that
the proposal contained in this rulemaking has the potential for
adversely affecting an entire class of airplanes--namely light to
medium business jets with trimmable stabilizers and unpowered
elevators. Many of these airplanes exhibit a mild control force
reversal from a push force to a pull force between zero g and 0.5 g.
Although such a characteristic will not comply with the proposed
rule, the airplane remains easily controllable. The proposed
requirement for a push force to be required down to a zero g load
factor would reduce the stabilizer incidence available for trimming the
airplane by two to four degrees. This would require either a 20 to 40
percent larger stabilizer or other design changes to compensate for the
reduction in stabilizer trim range. The supporters of alternative 1 to
Sec. 25.143(i)(2) do not believe that the cost of these changes is
justified by any safety benefit, as these airplanes are not the types
having ICTS accidents.
Furthermore, the proposed Sec. 25.143(i)(1) would require that
sandpaper ice be considered if the elevator is unpowered, regardless of
the ice protection system. Many of the current business jets are
equipped with anti-ice systems that prevent ice formation on the
stabilizer leading edge. Thus, the jets would be evaluated under more
critical assumptions (that is, with the anti-ice system off) than the
types that have had accidents.
Ice-contaminated tailplanes retain normal linear characteristics
until the onset of flow separation. The separation causes the hinge
moment coefficient to slope gradually from one level to another over a
range of 4 to 10 degrees AOA. With the elevator down, the hinge moment
coefficient changes sign at an AOA in this range, which results in the
control force reversal from a push to a pull. On a particular business
jet with a relatively small elevator, this results in a gradually
increasing pull force from 0 pounds at approximately 0.4 g to 25 pounds
at zero g.
On airplanes with large unpowered elevators, especially those with
long chord lengths, the elevator control forces resulting from a
stalled tail can be very high. These forces may even be too high for
the pilots to counteract. For example, assume the elevator dimensions
of the previous example are scaled up by a factor of 2. The elevator
chord is then doubled, the area is quadrupled, and the pilot must exert
8 times as much force on the control to move the elevator. If the
control force in the previous example were 25 pounds at zero g, the
control force for this larger elevator would be 200 pounds. These
examples illustrate how the size and design of elevators for certain
airplanes determine whether the control forces would be acceptable or
hazardous. The test criteria recommended for showing compliance with
the requirements proposed as alternative 1 to Sec. 25.143(i)(2) would
identify those airplanes with the hazardous characteristics. Therefore,
the supporters of alternative 1 to Sec. 25.143(i)(2) believe that
there is no difference in safety between this alternative and our
proposal.
Results of the National Aeronautics and Space Administration's
(NASA) Tailplane Icing Program provide a basis for evaluating whether
the proposed requirements adequately address the safety concerns.
Flight tests were conducted in which a test airplane performed a series
of pushovers and other maneuvers with and without ice accretions. Even
without ice accretions, reversed control forces were sometimes
experienced in the pushover maneuvers for some configurations. With the
ice accretions, control forces exceeding 100 pounds were experienced in
some of the pushovers although the airplane remained controllable. In
one test, a departure from controlled flight occurred during a power
transition with a critical ice accretion and flaps 40 (which is the
maximum landing flap configuration for this airplane). This event
involved a sudden nose-down pitch-over from 1-g flight like the ICTS
accident scenarios. The same ice accretion had degraded pushover
characteristics to the point that a 50-pound pull was required to
recover from zero g with flaps 10, and 100 pounds was required with
flaps 20. Accordingly, the criteria proposed as alternative 1 to Sec.
25.143(i)(2) provide an adequate safety margin, and would have
identified the aircraft as unacceptable before it ever got to the flaps
40 configuration at which it lost control.
We disagree with the position of the supporters of alternative 1 to
Sec. 25.143(i)(2) for the following reasons:
a. Ice contaminated tailplane stall/elevator hinge moment reversal
has been a significant factor in accidents occurring in icing
conditions. Rapid and large changes in pitch, significant changes in
control forces, pilot surprise, and possible disorientation in poor
visibility that can follow from a tailplane stall/elevator hinge moment
reversal can result in loss of pitch control. Coupled with the weather
conditions that lead to ICTS, this loss of control will usually occur
at low altitude where there is a higher probability of an accident.
b. Historically, the pushover test was usually performed to 0.5 g
load factor, although this was often done with a high pitch rate and,
hence, there was some overshoot of the 0.5 g load factor. A push force
on the elevator control was required to reach this g level.
Certification testing and service experience has since shown that
testing to only to 0.5 g is inadequate, considering the relatively high
frequency of experiencing 0.5 g in operations. Since the beginning of
the 1980s, the practice of many certification authorities has been to
require testing to lower load factors, and the JAA's Notice of Proposed
Amendment (NPA) 25F-219 requires a push force throughout the maneuver
to zero g.
c. Reversal of elevator control force versus normal acceleration is
not acceptable within the flight envelope. Existing requirements and
advisory material addressing elevator control force characteristics
(Sec. Sec. 25.143(f), 25.255(b)(2), and the guidance material to Sec.
25.143(f)) do not allow force reversals. Furthermore, a survey of FAA,
JAA, and other flight test personnel showed that a clear majority did
not favor anything less than a push force on the elevator control to
zero g.
Alternative 1 to Sec. 25.143(i)(2) would at least partially
address the cause of past ICTS accidents. However, the method proposed
for determining the acceptability of a control force reversal
[[Page 67292]]
is subjective and would lead to inconsistent evaluations. We maintain
that a push force to zero g with an ice-contaminated tailplane is the
minimum standard that can be accepted. Zero g is within the flight
envelope of the airplane and this criterion addresses the need to have
acceptable handling qualities for operational service when the pilot
would not expect any control force reversal. Requiring a push force to
zero g also removes subjectivity in the assessment of the airplane's
controllability and provides readily understood criteria of
acceptability. Any lesser standard would not give confidence that the
problem has been fully addressed.
Transport Canada proposed the following alternative as a compromise
between requiring a push force to either zero g or 0.5 g:
Transport Canada advisory material dating back to the mid-1980s
specified that applicants must demonstrate 0.5 g applied
to the longitudinal control. In practice, the demonstration was done in
a fairly abrupt maneuver that generated a significantly higher
transient pitch rate than that associated with a steady normal
acceleration. The minimum normal acceleration obtained was usually
around 0.25 g or less. It was considered that the pitch rate aspect was
just as important as the actual normal acceleration in determining
whether there were unsafe characteristics associated with tailplane
stall. No pass/fail criteria were provided in the Transport Canada
guidance except that the characteristics had to be satisfactory.
The accident record on ice contaminated tailplane stall indicates
that a significant factor was the pilot's startled reaction to an
abrupt hinge moment reversal and the magnitude of the control force
required to recover the airplane to a normal 1 g condition. Alternative
1 to Sec. 25.143(i)(2) would recognize this controllability issue by
limiting the amount of pull force required to promptly recover the
airplane from a zero g condition to a 50-pound pull force. In addition,
recognizing that positive stability is also important, alternative 1 to
Sec. 25.143(i)(2) would require a push force down to 0.5 g.
Accident data available to Transport Canada indicate that aircraft
involved in incidents and/or accidents incurred a tailplane stall at
approximately 0.3 g to 0.4 g. Based on this data and Transport Canada's
past practice, alternative 1 to Sec. 25.143(i)(2) would be acceptable,
except that the issue of pitch rate is not specifically identified in
the criteria. Transport Canada recognizes that combining pitch rate
with a normal acceleration in a requirement is probably too complex,
especially for the wide range of aircraft designs encompassed by part
25 and the parallel JAR-25 standards. Thus, Transport Canada considers
that, if the requirement would only specify a `g' level, then 0.5 g for
positive stability is inadequate. As a compromise, Transport Canada
proposes requiring a push force down to a value of 0.25 g as
alternative 2 to Sec. 25.143(i)(2).
While it is a compromise between the requirement proposed in this
rulemaking and alternative 1 (by specifying 0.25 g for the push force
requirement), we disagree with this alternative because it does not
fully address the safety concerns throughout the flight envelope. It
also does not fully address the cost concerns expressed within the
FTHWG regarding Sec. 25.143(i)(2) as proposed in this rulemaking.
The Transport Canada alternative recognizes the importance of pitch
rate. An abrupt nose-down control input is required to reach zero g. We
consider that testing to zero g, however, ensures that high pitch rates
are adequately evaluated without the added complication of specifying a
pitch rate requirement.
B. Non-Consensus Issue 2--Sec. 25.143(i)(3)
The proposed new Sec. 25.143(i)(3) would add a requirement that
any changes in longitudinal control force to maintain speed with
increasing sideslip angle be progressive with no reversals or
unacceptable discontinuities. The FTHWG did not reach a consensus on
whether it would be necessary to add a specific regulatory requirement
to address this issue. The majority of the FTHWG members felt that
there did not appear to be sufficient data to establish criteria
specific enough to stand as a regulatory requirement and proposed that
the issue be addressed through non-regulatory guidance material.
Anomalies in longitudinal control force during sideslip maneuvers
have been of concern to some accident investigators and regulatory
specialists. At one time, we proposed that pushover maneuvers be
conducted while in sideslips. Transport Canada considered that
performing sideslips in a pushover maneuver was excessive, but
recognizing the concern, proposed an additional requirement that would
specifically assess longitudinal control stick forces while in sideslip
maneuvers.
We consider that a consensus was reached on the need to address
this issue; the only difference appears to be whether it should be
addressed in advisory material or in the proposed rule. We consider
that this issue raises important safety concerns that must be addressed
as a specific evaluation requirement. Therefore, it is appropriate to
place it in the rule rather than in an AC. We recognize that AC
material may also be needed to provide guidance on an acceptable means
of compliance.
C. Non-Consensus Issue 3--Sec. Sec. 25.143(j)(1) and 25.207(h)
The proposed new Sec. Sec. 25.143(j)(1) and 25.207(h) would apply
different requirements when different means are used for the pilot to
visually recognize icing conditions. Compliance with all of the Sec.
25.143 controllability requirements for non-icing conditions would
apply if activation of the ice protection system depends on seeing a
specified ice accretion on a reference surface (for example, on an ice
accretion probe, or a wing leading edge). However, less stringent
requirements using a lesser ice accretion would apply to any other
means of identifying icing conditions, including seeing the first
indication of an ice accretion on a reference surface.
The FTHWG did not reach a consensus on the proposed Sec.
25.143(j)(1). The Air Line Pilots Association (ALPA), which was
represented in the FTHWG, disagrees with the proposal. The ALPA
considers visually recognizing the first indication of ice accreting on
a reference surface to be the same situation as visually recognizing a
specific amount of ice accretion on a reference surface. To the ALPA,
both are means of visual recognition that require the flightcrew to
monitor conditions outside the cockpit. Whenever it is necessary for
the pilots to check outside the cockpit (which the ALPA does not
consider to be equivalent to a primary instrument visual scan pattern),
the ALPA believes that the same basic maneuver capabilities, stall
protection requirements, and ice accretion amounts should apply.
The ALPA proposes the following alternative text for Sec.
25.143(j)(1):
``If normal operation of any ice protection system is dependent
upon visual recognition of ice accretion, the requirements of Sec.
25.143 are applicable with the ice accretion defined in proposed
appendix C, part II(e).''
The ALPA has similar concerns with the proposed Sec. 25.207(h)(1)
and proposes the following alternative text:
``If normal operation of any ice protection system is dependent
upon visual recognition of ice accretion, the requirements of this
section, except
[[Page 67293]]
paragraphs (c) and (d), are applicable with the ice accretion defined
in appendix C, part II(e).''
We disagree with the alternative proposals for Sec. Sec.
25.143(j)(1) and 25.207(h)(1).
The FTHWG found that there are significant differences in the
aerodynamic effects on an airplane between the two different means of
visual recognition of icing conditions identified in the ALPA
alternative proposal discussion. The best example of the means covered
by Sec. Sec. 25.143(j)(1) and 25.207(h)(1), as proposed in this
notice, are airplanes with pneumatic deicing boots. The operating
procedures call for a specified amount of ice build-up before
activating the ice protection system, a process that is repeated often
during an icing encounter. In this case, the airplane is assured of
being operated with some level of aerodynamic degradation before
activation of the ice protection system.
The best example of the second type of visual recognition of icing
conditions are airplane models that are equipped with an ice accretion
probe in the pilot's field of view outside the airplane. The published
procedure calls for activating the ice protection system at the first
indication of ice buildup on the accretion probe. Such accretion
probes, or an equivalent such as a windshield wiper post, are highly
efficient ice collectors, and typically will accrete visible ice prior
to ice accretion on aerodynamic surfaces. Under this means of detecting
icing conditions, there may be little or no ice buildup on aerodynamic
surfaces before activation and normal operation of the ice protection
system, and little or no aerodynamic degradation. These two means of
visually recognizing that icing conditions are present are distinctly
different.
D. Non-Consensus Issue 4--Appendix C
The ALPA representative on the FTHWG did not consider that the
combination of the proposed regulatory changes and associated proposed
advisory material provided a definitive enough description of the
required ice accretions, particularly with regard to the variables that
must be considered in determining the critical ice accretion for a
particular flight phase. The ALPA alternative proposal recommends
adding specific references to ``all flight conditions within the
operational limits of the airplane'' and ``configuration changes'' to
the general ice accretion requirements of proposed part II(a) of
appendix C to ensure that the full range of possible accretion
locations for atmospheric conditions are considered. The alternative
text would read:
Section 25.21(g) states that if certification for flight in
icing conditions is desired, the applicable requirements of subpart
B must be met in the icing conditions of appendix C, unless
otherwise prescribed. The most critical ice accretion in terms of
handling characteristics and performance for each flight phase must
be determined, taking into consideration the atmospheric conditions
of part I of this appendix, and all flight conditions within the
operational limits of the airplane (for example, configuration,
configuration changes, speed, angle-of-attack, and altitude). The
following ice accretions must be determined:
The NASA research following the Model ATR-72 accident at Roselawn,
Indiana, in 1994, observed that decreasing AOA causes an increase in
aft ice accretion limit on the upper surface of an airfoil. Likewise,
the fact that airflow separation on the negative pressure side (upper
surface for a typical wing) is caused by ice accretions on the upper
surface is discussed. Research performed by Dr. Michael B. Bragg and
others at the University of Illinois has demonstrated significant
variation in the effects on airfoil aerodynamics of a simulated ice
accretion depending upon its location on the negative pressure side of
the airfoil.
Differing airspeeds and high lift device configurations
significantly change the AOA and, consequently, the location of the
stagnation point around which any ice accretion forms on an airfoil.
For normal operation, this should make no difference on surfaces that
are protected by the icing system. But for unprotected surfaces, in the
failure case and for ice that accumulates prior to normal system
operation, changing the location of ice on the negative pressure side
of the airfoil may be significant. Procedural restrictions (that is, no
holding with flaps extended, speed or configuration restrictions in
case of ice system failure, etc.) could be used to limit the
configurations necessary to determine the most critical ice accretion.
However, the full range of possible accumulation locations must be
considered.
In their report on the Embraer Model EMB 120 accident at Monroe,
Michigan, in 1997, the NTSB concluded that:
The icing certification process has been inadequate because it
has not required manufacturers to demonstrate the airplane's flight
handling and stall characteristics under a sufficiently realistic
range of adverse accretion/flight handling conditions. (Finding
27)
The recommendations submitted by the FTHWG, and this proposed rule,
consider ice accretions for all phases of flight and all configurations
of high lift devices. The proposed rule would require consideration of
the effects of the ice accretion during the phases of flight with high
lift devices extended. The associated proposed advisory material
specifically recommends that natural icing flight testing with high
lift devices extended in the approach and landing conditions be
conducted.
We do not concur with the alternative discussed above. The research
referred to above determined the effect on lift and drag of a spoiler-
like shape located at various chord locations of a two dimensional
airfoil. (A two dimensional airfoil is a wing with an infinite
wingspan, that is, there are no wingtips. It is common practice for
wind tunnel testing to use wings that span the test section from one
wall of the wind tunnel to the other. Results obtained for a two
dimensional airfoil must usually be adjusted to properly represent a
real wing.) These data do not support the alternative position because
no data were presented in the references to connect either this shape
or its location with airplane flight conditions or icing conditions,
either inside or outside of proposed appendix C. There were no data
showing the effect of the shape on an airfoil with high lift devices
extended.
The effect of any shape on a two-dimensional airfoil is much larger
than the effect of a similar shape on a complete airplane with high
lift devices extended, and the effect of such a shape diminishes with
increasing airplane size.
The effect of ice accretions similar to the shapes tested in the
referenced report were also considered by the FTHWG when it discussed
ice accreted in conditions outside of proposed appendix C. The majority
of the FTHWG recommended not including these accretions in the
recommendations because the only icing design envelope available is
proposed appendix C.
IV. Rulemaking Notices and Analyses
Paperwork Reduction Act
The Paperwork Reduction Act of 1995 (44 U.S.C. 3507(d)) requires
that the FAA to consider the impact of paperwork and other information
collection burdens imposed on the public. We have determined that there
are no current new information collection requirements associated with
this proposed rule.
International Compatibility
In keeping with U.S. obligations under the Convention on
International
[[Page 67294]]
Civil Aviation, it is FAA policy to comply with International Civil
Aviation Organization (ICAO) Standards and Recommended Practices to the
maximum extent practicable. The FAA has determined that there are no
ICAO Standards and Recommended Practices that correspond to these
proposed regulations.
Executive Order 13132, Federalism
The FAA analyzed this proposed rule under the principles and
criteria of Executive Order 13132, Federalism. We determined that this
action would not have a substantial direct effect on the States, on the
relationship between the national Government and the States, or on the
distribution of power and responsibilities among the various levels of
government, and therefore would not have federalism implications.
Regulatory Evaluation, Regulatory Flexibility Determination,
International Trade Impact Assessment, and Unfunded Mandates Assessment
This portion of the preamble summarizes the FAA's analysis of the
economic impacts of a proposed rule amending part 25 of 14 CFR to
change the regulations applicable to transport category airplanes
certificated for flight in icing conditions. It also includes summaries
of the initial regulatory flexibility determination. We suggest readers
seeking greater detail read the full regulatory evaluation, which is in
the docket for this rulemaking.
Introduction
Changes to Federal regulations must undergo several economic
analyses. First, Executive Order 12866 directs that each Federal agency
propose or adopt a regulation only upon a reasoned determination that
the benefits of the intended regulation justify its costs. Second, the
Regulatory Flexibility Act of 1980 requires agencies to analyze the
economic impact of regulatory changes on small entities. Third, the
Trade Agreements Act (19 U.S.C. 2531-2533) prohibits agencies from
setting standards that create unnecessary obstacles to the foreign
commerce of the United States. In developing U.S. standards, this Trade
Act requires agencies to consider international standards and, where
appropriate, to be the basis of U.S. standards. Fourth, the Unfunded
Mandates Reform Act of 1995 (Pub. L. 104-4) requires agencies to
prepare a written assessment of the costs, benefits, and other effects
of proposed or final rules that include a Federal mandate likely to
result in the expenditure by State, local, or tribal governments, in
the aggregate, or by the private sector, of $100 million or more
annually (adjusted for inflation).
In conducting these analyses, FAA has determined this rule (1) has
benefits that justify its costs, (2) is not a ``significant regulatory
action'' as defined in section 3(f) of Executive Order 12866, and is
not ``significant'' as defined in DOT's Regulatory Policies and
Procedures; (3) would not have a significant economic impact on a
substantial number of small entities; (4) would have a neutral impact
on international trade; and (5) does not impose an unfunded mandate on
state, local, or tribal governments, or on the private sector. These
analyses, available in the docket, are summarized below.
Total Benefits and Costs of This Rulemaking
The estimated cost of this proposed rule is $66.4 million ($22.0
million in present value at seven percent). The estimated potential
benefits of avoiding 13 fatalities are $89.9 million ($23.7 million in
present value at seven percent).
Who Is Potentially Affected by This Rulemaking
Operators of part 25 U.S.-registered aircraft conducting
operations under 14 CFR parts 121, 129, 135, and
Manufacturers of those part 25 aircraft.
Our Cost Assumptions and Sources of Information
This evaluation makes the following assumptions:
The base year is 2003.
This proposed rule is assumed to become a final rule in 2
years, and will then be effective immediately.
The production run for newly certificated airplane models
is 20 years.
The average life of an airplane is 25 years.
We analyzed the costs and benefits of this proposed rule
over the 45-year period (20 + 25 = 45) 2005 through 2049.
We used a 10-year certification compliance period. For the
10-year life-cycle period, the FAA calculated an average of four new
certifications would occur.
We performed sensitivity analysis on present value
discount rates of one, three, and the base case seven percent.
New airplane certifications will occur in year one of the
analysis time period.
Value of fatality avoided--$3.0 million (Source:
``Treatment of Value of Life and Injury In Economic Analysis,'' (FAA
APO Bulletin, February 2002).)
Benefits of This Rulemaking
The benefits of this proposed rule consist of the value of lives
saved due to avoiding accidents involving part 25 airplanes operating
in icing conditions. We estimate that a total of 13 fatalities could
potentially be avoided by adopting the proposed rule. We use $3.0
million as the value of an avoided fatality. Over the 45-year period of
analysis, the potential benefit of the proposed rule would be $89.9
million ($23.7 million in present value at seven percent).
Cost of This Rulemaking
We estimate the costs of this proposed rule to be about $66.4
million ($22.0 million in present value at seven percent) over the 45-
year analysis period. The total cost of $66.4 million equals the fixed
certification costs of $6.7 million incurred in the first year plus the
variable annual fuel burn cost of $59.7 million.
Regulatory Flexibility Determination
The Regulatory Flexibility Act of 1980 (RFA) establishes ``as a
principle of regulatory issuance that agencies shall endeavor,
consistent with the objective of the rule and of applicable statutes,
to fit regulatory and informational requirements to the scale of the
business, organizations, and governmental jurisdictions subject to
regulation.'' To achieve that principle, the RFA requires agencies to
solicit and consider flexible regulatory proposals and to explain the
rationale for their actions. The RFA covers a wide-range of small
entities, including small businesses, not-for-profit organizations and
small governmental jurisdictions.
Agencies must perform a review to determine whether a proposed or
final rule will have a significant economic impact on a substantial
number of small entities. If the agency determines that it will, the
agency must prepare a regulatory flexibility analysis as described in
the Act.
However, if an agency determines that a proposed or final rule is
not expected to have a significant economic impact on a substantial
number of small entities, section 605(b) of the 1980 RFA provides that
the head of the agency may so certify and a regulatory flexibility
analysis is not required. The certification must include a statement
providing the factual basis for this determination, and the reasoning
should be clear. This proposed rule would not have a significant
economic impact on a substantial number of small entities.
[[Page 67295]]
International Trade Impact Assessment
The Trade Agreement Act of 1979 prohibits Federal agencies from
establishing any standards or engaging in related activities that
create unnecessary obstacles to the foreign commerce of the United
States. Legitimate domestic objectives, such as safety, are not
considered unnecessary obstacles. The statute also requires
consideration of international standards and, where appropriate, that
they be the basis for U.S. standards. The FAA has assessed the
potential effect of this proposed rule and determined that it would
impose the same costs on domestic and international entities and thus
have a neutral trade impact.
Unfunded Mandates Assessment
The Unfunded Mandates Reform Act of 1995 (the Act) is intended,
among other things, to curb the practice of imposing unfunded Federal
mandates on State, local, and tribal governments. Title II of the Act
requires each Federal agency to prepare a written statement assessing
the effects of any Federal mandate in a proposed or final agency rule
that may result in an expenditure of $100 million or more (adjusted
annually for inflation) in any one year by State, local, and tribal
governments, in the aggregate, or by the private sector; such a mandate
is deemed to be a ``significant regulatory action.'' The FAA currently
uses an inflation-adjusted value of $120.7 million in lieu of $100
million. This proposed rule does not contain such a mandate. The
requirements of Title II of the Act, therefore, do not apply.
Regulations Affecting Intrastate Aviation in Alaska
Section 1205 of the FAA Reauthorization Act of 1996 (110 Stat.
3213) requires the Administrator, when modifying regulations in Title
14 of the CFR in a manner affecting intrastate aviation in Alaska, to
consider the extent to which Alaska is not served by transportation
modes other than aviation, and to establish such regulatory
distinctions as he or she considers appropriate. Because this proposed
rule would apply to the certification of future designs of transport
category airplanes and their subsequent operation, it could, if
adopted, affect intrastate aviation in Alaska. The FAA therefore
specifically requests comments on whether there is justification for
applying the proposed rule differently in intrastate operations in
Alaska.
Plain Language
Executive Order 12866 (58 FR 51735, Oct. 4, 1993) requires each
agency to write regulations that are simple and easy to understand. We
invite your comments on how to make these proposed regulations easier
to understand, including answers to questions such as the following:
Are the requirements in the proposed regulations clearly stated?
Do the proposed regulations contain unnecessary technical
language or jargon that interferes with their clarity?
Would the proposed regulations be easier to understand if
they were divided into more (but shorter) sections?
Is the description in the NPRM preamble helpful in
understanding the proposed regulations?
Please send your comments to the address specified in the FOR
FURTHER INFORMATION CONTACT section. [new template uses ADDRESSES]
Environmental Analysis
FAA Order 1050.1E identifies FAA actions that are categorically
excluded from preparation of an environmental assessment or
environmental impact statement under the National Environmental Policy
Act in the absence of extraordinary circumstances. The FAA has
determined this proposed rulemaking action qualifies for the
categorical exclusion identified in paragraph number 312f and involves
no extraordinary circumstances.
Regulations That Significantly Affect Energy Supply, Distribution, or
Use
The FAA has analyzed this NPRM under Executive Order 13211, Actions
Concerning Regulations that Significantly Affect Energy Supply,
Distribution, or Use (May 18, 2001). We have determined that it is not
a ``significant energy action'' under the executive order because it is
not a ``significant regulatory action'' under Executive Order 12866,
and it is not likely to have a significant adverse effect on the
supply, distribution, or use of energy.
V. Appendixes to the Preamble
Appendix I.--List of Acronyms Used in This Document
[For your reference and ease of reading, the following list defines the
acronyms that are used throughout this document. This appendix will not
appear in the Code of Federal Regulations.]
------------------------------------------------------------------------
Acronym Definition
------------------------------------------------------------------------
AC................................... Advisory Circular.
ACJ.................................. Advisory Circular Joint (issued
by JAA).
AFM.................................. Airplane Flight Manual.
ALPA................................. Air Line Pilots Association.
AMJ.................................. Advisory Material Joint (issued
by JAA).
AOA.................................. Angle-of-Attack.
ARAC................................. Aviation Rulemaking Advisory
Committee.
CAS.................................. Calibrated Airspeed.
CS................................... Certification Specifications
(EASA airworthiness standards).
EASA................................. European Aviation Safety Agency.
FAA.................................. Federal Aviation Administration.
FTHWG................................ Flight Test Harmonization Working
Group.
ICTS................................. Ice-Contaminated Tailplane Stall.
IPHWG................................ Ice Protection Harmonization
Working Group.
JAA.................................. Joint Aviation Authorities.
JAR.................................. Joint Aviation Requirements (JAA
airworthiness standards).
LFE.................................. Limit Flight Envelope.
NASA................................. National Aeronautics and Space
Administration.
NFE.................................. Normal Flight Envelope.
NPA.................................. Notice of Proposed Amendment
(issued by JAA or EASA).
NPRM................................. Notice of Proposed Rulemaking.
NTSB................................. National Transportation Safety
Board.
OFE.................................. Operational Flight Envelope.
[[Page 67296]]
SLD.................................. Supercooled Large Drop.
V1................................... The maximum speed in the takeoff
at which the pilot must take the
first action (for example, apply
brakes, reduce thrust, deploy
speed brakes) to stop the
airplane within the accelerate-
stop distance. V1 also means the
minimum speed in the takeoff,
following a failure of the
critical engine at VEF, at which
the pilot can continue the
takeoff and achieve the required
height above the takeoff surface
within the takeoff distance.
V2................................... Takeoff Safety Speed. (The target
speed to be reached by the time
the airplane is 35 feet above
the takeoff surface.)
VDF/MDF.............................. Demonstrated Flight Diving Speed.
VEF.................................. Engine Failure Speed. The speed
at which the critical engine is
assumed to fail during takeoff.
VFC/MFC.............................. Maximum Speed for Stability
Characteristics.
VFE.................................. Maximum Flaps Extended Speed.
VFTO................................. Final Takeoff Speed. The speed at
which compliance is shown with
the final takeoff climb gradient
requirements of Sec.
25.121(c).
VMC.................................. Minimum Control Speed with the
critical engine inoperative.
VMCA................................. Air Minimum Control Speed.
(Commonly used terminology for
VMC.)
VMCG................................. Ground Minimum Control Speed.
VMCL................................. Landing Minimum Control Speed.
VMO/MMO.............................. Maximum Operating Limit Speed.
VMU.................................. Minimum Unstick Speed. The
minimum airspeed at and above
which the airplane can safely
lift off the ground and continue
the takeoff.
VR................................... Rotation Speed. The speed at
which the pilot first makes an
input to the airplane controls
to rotate the airplane to the
takeoff pitch attitude.
VREF................................. Landing Reference Speed.
VS 1 g............................... 1-g Stall Speed. The calibrated
airspeed at which aerodynamic
forces alone can support the
airplane in 1-g flight.
VSR.................................. Reference Stall Speed. VSR may
not be less than VS 1 g. For
airplanes with a device that
abruptly pushes the nose down at
a selected angle of attack, (for
example, a stick pusher), VSR
may not be less than 2 knots or
2 percent, whichever is greater,
above the speed at which the
device operates.
VSR0................................. Reference Stall Speed in the
landing configuration.
------------------------------------------------------------------------
Appendix 2.--List of Terms Used in This NPRM
[For the reader's reference and ease of reading, the following list
defines terms that are used throughout this document. This appendix will
not appear in the Code of Federal Regulations.]
------------------------------------------------------------------------
Term Definition
------------------------------------------------------------------------
Airfoil........................................... The shape of the
wing when looking
at its profile.
Airplane handling qualities....................... The response of the
airplane to control
inputs as assessed
primarily by a
pilot evaluating
the ease of
accomplishing
maneuvering tasks.
Airplane handling
qualities refer to
the stability,
controllability,
and maneuverability
of the airplane.
Airplane performance.............................. The capability of
the airplane in
terms of speeds,
distances, weights,
flight paths, etc.,
expressed in terms
of characteristics
like takeoff and
landing distances,
en route altitude
capability, climb
and descent rates,
flight paths, fuel
burn, payload
capability, range,
etc.
En route ice...................................... The critical ice
accretion
appropriate to
normal operation of
the ice protection
system during the
en route phase of
flight.
Final takeoff ice................................. The most critical
ice accretion
appropriate to
normal operation of
the ice protection
system during the
final takeoff
segment. Ice
accretion is
assumed to start at
liftoff in the
takeoff maximum
icing conditions of
14 CFR part 25,
appendix C, part 1,
paragraph (c).
Force reversal.................................... A reversal in the
direction of the
force that the
pilot needs to
apply to perform a
specified maneuver
or achieve a
specified load
factor. For
example, in a
maneuver to reduce
the load factor, a
push force on the
pitch control is
initially needed to
begin the maneuver,
but changes to a
pull force as the
load factor is
reduced.
Holding ice....................................... The critical ice
accretion
appropriate to
normal operation of
the ice protection
system during the
holding phase of
flight.
Hinge moment...................................... The rotational force
about the hinge of
a control surface.
Depending on the
design of the
airplane's flight
control system,
large hinge moments
can result in large
forces at the
pilot's control,
and hinge moment
reversals can
result in forces
reversals.
Ice-contaminated tailplane stall.................. Ice accretions on
the tailplane
leading to either
completely stalled
airflow over the
horizontal
stabilizer, or an
elevator hinge
moment reversal due
to separated flow
on the lower
surface of the
horizontal
stabilizer.
Landing ice....................................... The critical ice
accretion
appropriate to
normal operation of
the ice protection
system during the
landing phase of
flight. This is
usually the same as
holding ice.
Load factor....................................... The lift divided by
the weight,
expressed in units
of gravity, or
``g.'' For example,
in straight and
level flight, the
lift equals the
weight and the load
factor is 1 g.
Pushover maneuver................................. A maneuver resulting
from the pilot
applying a push
force to the
airplane pitch
control to pitch
the airplane's nose
down.
Sandpaper ice..................................... A thin, rough layer
of ice.
Stall............................................. Loss of lift caused
by the airflow
becoming detached
from the upper
surface of a
lifting surface
such as a wing or
tailplane.
[[Page 67297]]
Takeoff ice....................................... The critical ice
accretion
appropriate to
normal operation of
the ice protection
system during the
takeoff phase of
flight, assuming
accretion starts at
liftoff in the
takeoff maximum
icing conditions of
14 CFR part 25,
appendix C, part 1,
paragraph (c).
Tailplane......................................... The horizontal wing
attached to the
tail assembly of
the airplane.
------------------------------------------------------------------------
Appendix 3: Relevant NTSB Recommendations
If adopted, this rulemaking would respond to the following
National Transportation Safety Board (NTSB) Safety Recommendations.
1. Safety Recommendation A-91-87. ``Amend the icing
certification rules to require flight tests wherein ice is
accumulated in those cruise and approach flap configurations in
which extensive exposure to icing conditions can be expected, and
require subsequent changes in configuration, to include landing
flaps.'' [complete text available in the docket]
This safety recommendation resulted from an accident on December
26, 1989, at Pasco, Washington, where the airplane stalled due to
ice-contamination on the tailplane.\6\ The radar data revealed that
the airplane was in the clouds in icing conditions for almost 9\1/2\
minutes. The NTSB determined that the probable cause of this
accident was the flightcrew's decision to continue an unstabilized
ILS approach that led to a stall, most likely of the horizontal
stabilizer, and loss of control at low altitude. Contributing to the
stall and loss of control was the accumulation of airframe ice that
degraded the aerodynamic performance of the airplane.\7\ The
airplane was destroyed and the two pilots and all four passengers
received fatal injuries. As discussed in more detail later, this
notice proposes to require applicants to demonstrate during type
certification that their airplane is not susceptible to ice-
contaminated tailplane stall.
---------------------------------------------------------------------------
\6\ United Express flight 2415 (Sundance 415), a British
Aerospace BA-3101 Jetstream, operated by NPA Inc., (NPA is the name
of the airline and is not an abbreviation).
\7\ ``Effect of Ice on Aircraft Handling Characteristics (1984
Trials),'' Jetstream 31--G-JSSD, British Aerospace Flight Test
Report FTR.177/JM, dated May 13, 1985.
---------------------------------------------------------------------------
2. Safety Recommendation A-98-94. ``Require manufacturers of all
turbine-engine driven airplanes (including the EMB-120) to provide
minimum maneuvering airspeed information for all airplane
configurations, phases, and conditions of flight (icing and non-
icing conditions); minimum airspeeds also should take into
consideration the effects of various types, amounts, and locations
of ice accumulations, including thin amounts of very rough ice, ice
accumulated in supercooled large droplet icing conditions, and
tailplane icing.'' [complete text available on the NTSB Web site at:
http://ntsb.gov/Recs/letters/1998/A98_88_106.pdf]
This safety recommendation resulted from an accident on January
9, 1997, near Monroe, Michigan.\8\ In that accident, the flightcrew
were attempting a turning maneuver and did not know there was ice on
the wing's leading edge. With the degraded aerodynamics due to the
ice on the wing's leading edge, the airplane was at too low an
airspeed to conduct the turning maneuver without stalling. This
caused a rapid descent after an uncommanded roll excursion,
resulting in a crash. The airplane was destroyed and the 2 flight
crewmembers, 1 flight attendant, and 26 passengers all died. The
NTSB determined that the probable cause of this accident was the
FAA's failure to establish adequate aircraft certification standards
for flight in icing conditions, and to require the establishment of
adequate minimum airspeed for icing conditions.\9\
---------------------------------------------------------------------------
\8\ Comair flight 3272, Empresa Brasileira de Aeronautica, S/A
(Embraer) EMB-120, operated by COMAIR Airlines, Inc.
\9\ National Transportation Safety Board, 1998. ``In-Flight
Icing Encounter and Uncontrolled Collision With Terrain, Comair
Flight 3272, Embraer EMB-120RT, N265CA, Monroe, Michigan, January 9,
1997.'' Aircraft Accident Report NTSB/AR-98/04. Washington, DC.
---------------------------------------------------------------------------
As discussed in more detail later, this notice proposes to
require applicants to demonstrate during type certification that
their airplane has adequate maneuvering capabilities in icing
conditions. The requirements added to part 25 by the 1-g stall rule
\10\ and the requirements proposed in this NPRM would ensure that
the minimum operating speeds determined during the certification of
all future transport category airplanes provide adequate maneuver
capability in both non-icing and icing conditions.
---------------------------------------------------------------------------
\10\ Docket No. FAA-2002-13982, published in the Federal
Register (67 FR 70812, November 26, 2002).
---------------------------------------------------------------------------
3. Safety Recommendation A-98-96. ``Require the manufacturers
and operators of all airplanes that are certificated to operate in
icing conditions to install stall warning/protection systems that
provide a cockpit warning (aural warning and/or stick shaker) before
the onset of stall when the airplane is operating in icing
conditions.'' [complete text available on the NTSB Web site at:
http://ntsb.gov/Recs/letters/1998/A98_88_106.pdf]
This safety recommendation resulted from the same accident
discussed under Safety Recommendation A-98-94, above. The airplane
stalled before either the stall warning system or the stall
protection system activated. As discussed in more detail later, this
notice proposes to require applicants to demonstrate during type
certification that their airplane provides adequate warning of an
impending stall in icing conditions.
Although we do not currently have a part 25 regulatory
requirement for stall warning to be provided by a warning device in
the cockpit, general industry design practice is to use a device
called a stick shaker to shake the control column to warn the pilot
of an impending stall.
XIV. Proposed Amendment
List of Subjects in 14 CFR Part 25:
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
The Proposed Amendment
In consideration of the foregoing, the Federal Aviation
Administration proposes to amend part 25 of Title 14, Code of Federal
Regulations, as follows:
PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES
1. The authority citation for part 25 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, and 44704
2. Amend Sec. 25.21 by adding a new paragraph (g) to read as
follows:
Sec. 25.21 Proof of compliance.
* * * * *
(g) The requirements of this subpart associated with icing
conditions apply only if certification for flight in icing conditions
is desired. If certification for flight in icing conditions is desired,
the following requirements also apply:
(1) Each requirement of this subpart, except Sec. Sec. 25.121(a),
25.123(c), 25.143(b)(1) and (b)(2), 25.149, 25.201(c)(2), 25.207(c) and
(d), 25.239, and 25.251(b) through (e), must be met in icing
conditions. Compliance must be shown using the ice accretions defined
in appendix C, assuming normal operation of the airplane and its ice
protection system in accordance with the operating limitations and
operating procedures established by the applicant and provided in the
Airplane Flight Manual.
(2) No changes in the load distribution limits of Sec. 25.23, the
weight limits of Sec. 25.25 (except where limited by performance
requirements of this
[[Page 67298]]
subpart), and the center of gravity limits of Sec. 25.27, from those
for non-icing conditions, are allowed for flight in icing conditions or
with ice accretion.
3. Amend Sec. 25.103 by revising paragraph (b)(3) to read as
follows:
Sec. 25.103 Stall speed.
* * * * *
(b) * * *
(3) The airplane in other respects (such as flaps, landing gear,
and ice accretions) in the condition existing in the test or
performance standard in which VSR is being used;
* * * * *
4. Amend Sec. 25.105 by revising paragraph (a) to read as follows:
Sec. 25.105 Takeoff.
(a) The takeoff speeds prescribed by Sec. 25.107, the accelerate-
stop distance prescribed by Sec. 25.109, the takeoff path prescribed
by Sec. 25.111, the takeoff distance and takeoff run prescribed by
Sec. 25.113, and the net takeoff flight path prescribed by Sec.
25.115, must be determined in the selected configuration for takeoff at
each weight, altitude, and ambient temperature within the operational
limits selected by the applicant--
(1) In non-icing conditions; and
(2) In icing conditions, if in the configuration of Sec. 25.121(b)
with the takeoff ice accretion defined in appendix C:
(i) The stall speed at maximum takeoff weight exceeds that in non-
icing conditions by more than the greater of 3 knots CAS or 3 percent
of VSR; or
(ii) The degradation of the gradient of climb determined in
accordance with Sec. 25.121(b) is greater than one-half of the
applicable actual-to-net takeoff flight path gradient reduction defined
in Sec. 25.115(b).
* * * * *
5. Amend Sec. 25.107 by revising paragraph (c)(3) and (g)(2) and
adding new paragraph (h) to read as follows:
Sec. 25.107 Takeoff speeds.
* * * * *
(c) * * *
(3) A speed that provides the maneuvering capability specified in
Sec. 25.143(h).
* * * * *
(g) * * *
(2) A speed that provides the maneuvering capability specified in
Sec. 25.143(h).
(h) In determining the takeoff speeds V1, VR,
and V2 for flight in icing conditions, the values of
VMCG, VMC, and VMU determined for non-
icing conditions may be used.
6. Amend Sec. 25.111 by revising paragraph (c)(3)(iii), (c)(4),
and adding a new paragraph (c)(5) to read as follows:
Sec. 25.111 Takeoff path.
* * * * *
(c) * * *
(3) * * *
(iii) 1.7 percent for four-engine airplanes.
(4) The airplane configuration may not be changed, except for gear
retraction and automatic propeller feathering, and no change in power
or thrust that requires action by the pilot may be made until the
airplane is 400 feet above the takeoff surface; and
(5) If Sec. 25.105(a)(2) requires the takeoff path to be
determined for flight in icing conditions, the airborne part of the
takeoff must be based on the airplane drag:
(i) With the takeoff ice accretion defined in appendix C, from a
height of 35 feet above the takeoff surface up to the point where the
airplane is 400 feet above the takeoff surface; and
(ii) With the final takeoff ice accretion defined in appendix C,
from the point where the airplane is 400 feet above the takeoff surface
to the end of the takeoff path.
* * * * *
7. Revise Sec. 25.119 to read as follows:
Sec. 25.119 Landing climb: All-engines-operating.
In the landing configuration, the steady gradient of climb may not
be less than 3.2 percent, with the engines at the power or thrust that
is available 8 seconds after initiation of movement of the power or
thrust controls from the minimum flight idle to the go-around power or
thrust setting--
(a) In non-icing conditions, with a climb speed of VREF
determined in accordance with Sec. 25.125(b)(2)(i); and
(b) In icing conditions with the landing ice accretion defined in
appendix C, and with a climb speed of VREF determined in
accordance with Sec. 25.125(b)(2)(ii).
8. Amend Sec. 25.121 by revising paragraphs (b), (c), and (d) to
read as follows:
Sec. 25.121 Climb: One-engine inoperative.
* * * * *
(b) Takeoff; landing gear retracted. In the takeoff configuration
existing at the point of the flight path at which the landing gear is
fully retracted, and in the configuration used in Sec. 25.111 but
without ground effect:
(1) The steady gradient of climb may not be less than 2.4 percent
for two-engine airplanes, 2.7 percent for three-engine airplanes, and
3.0 percent for four-engine airplanes, at V2 with:
(i) The critical engine inoperative, the remaining engines at the
takeoff power or thrust available at the time the landing gear is fully
retracted, determined under Sec. 25.111, unless there is a more
critical power operating condition existing later along the flight path
but before the point where the airplane reaches a height of 400 feet
above the takeoff surface; and
(ii) The weight equal to the weight existing when the airplane's
landing gear is fully retracted, determined under Sec. 25.111.
(2) The requirements of paragraph (b)(1) of this section must be
met:
(i) In non-icing conditions; and
(ii) In icing conditions with the takeoff ice accretion defined in
appendix C, if in the configuration of Sec. 25.121(b) with the takeoff
ice accretion:
(A) The stall speed at maximum takeoff weight exceeds that in non-
icing conditions by more than the greater of 3 knots CAS or 3 percent
of VSR; or
(B) The degradation of the gradient of climb determined in
accordance with Sec. 25.121(b) is greater than one-half of the
applicable actual-to-net takeoff flight path gradient reduction defined
in Sec. 25.115(b).
(c) Final takeoff. In the en route configuration at the end of the
takeoff path determined in accordance with Sec. 25.111:
(1) The steady gradient of climb may not be less than 1.2 percent
for two-engine airplanes, 1.5 percent for three-engine airplanes, and
1.7 percent for four-engine airplanes, at VFTO with--
(i) The critical engine inoperative and the remaining engines at
the available maximum continuous power or thrust; and
(ii) The weight equal to the weight existing at the end of the
takeoff path, determined under Sec. 25.111.
(2) The requirements of paragraph (c)(1) of this section must be
met:
(i) In non-icing conditions; and
(ii) In icing conditions with the final takeoff ice accretion
defined in appendix C, if in the configuration of Sec. 25.121(b) with
the takeoff ice accretion:
(A) The stall speed at maximum takeoff weight exceeds that in non-
icing conditions by more than the greater of 3 knots CAS or 3 percent
of VSR; or
(B) The degradation of the gradient of climb determined in
accordance with Sec. 25.121(b) is greater than one-half of the
applicable actual-to-net takeoff flight path gradient reduction defined
in Sec. 25.115(b).
(d) Approach. In a configuration corresponding to the normal all-
engines-operating procedure in which VSR for
[[Page 67299]]
this configuration does not exceed 110 percent of the VSR
for the related all-engines-operating landing configuration:
(1) The steady gradient of climb may not be less than 2.1 percent
for two-engine airplanes, 2.4 percent for three-engine airplanes, and
2.7 percent for four-engine airplanes, with--
(i) The critical engine inoperative, the remaining engines at the
go-around power or thrust setting;
(ii) The maximum landing weight;
(iii) A climb speed established in connection with normal landing
procedures, but not exceeding 1.4 VSR; and
(iv) Landing gear retracted.
(2) The requirements of paragraph (d)(1) of this section must be
met:
(i) In non-icing conditions; and
(ii) In icing conditions with the holding ice accretion defined in
appendix C. The climb speed selected for non-icing conditions may be
used if the climb speed for icing conditions, computed in accordance
with paragraph (d)(1)(iii) of this section, does not exceed that for
non-icing conditions by more than the greater of 3 knots CAS or 3
percent.
9. Amend Sec. 25.123 by revising paragraphs (a) introductory text
and (b) to read as follows:
Sec. 25.123 En route flight paths.
(a) For the en route configuration, the flight paths prescribed in
paragraph (b) and (c) of this section must be determined at each
weight, altitude, and ambient temperature, within the operating limits
established for the airplane. The variation of weight along the flight
path, accounting for the progressive consumption of fuel and oil by the
operating engines, may be included in the computation. The flight paths
must be determined at a speed not less than VFTO, with--
* * * * *
(b) The one-engine-inoperative net flight path data must represent
the actual climb performance diminished by a gradient of climb of 1.1
percent for two-engine airplanes, 1.4 percent for three-engine
airplanes, and 1.6 percent for four-engine airplanes--
(1) In non-icing conditions; and
(2) In icing conditions with the en route ice accretion defined in
appendix C, if:
(i) A speed of 1.18 VSR with the en route ice accretion
exceeds the en route speed selected for non-icing conditions by more
than the greater of 3 knots CAS or 3 percent of VSR; or
(ii) The degradation of the gradient of climb is greater than one-
half of the applicable actual-to-net flight path reduction defined in
paragraph (b) of this section.
* * * * *
10. Revise Sec. 25.125 to read as follows:
Sec. 25.125 Landing.
(a) The horizontal distance necessary to land and to come to a
complete stop (or to a speed of approximately 3 knots for water
landings) from a point 50 feet above the landing surface must be
determined (for standard temperatures, at each weight, altitude, and
wind within the operational limits established by the applicant for the
airplane):
(1) In non-icing conditions; and
(2) In icing conditions with the landing ice accretion defined in
appendix C if VREF for icing conditions exceeds
VREF for non-icing conditions by more than 5 knots CAS.
(b) In determining the distance in (a):
(1) The airplane must be in the landing configuration.
(2) A stabilized approach, with a calibrated airspeed of not less
than VREF, must be maintained down to the 50-foot height.
(i) In non-icing conditions, VREF may not be less than:
(A) 1.23 VSR0;
(B) VMCL established under Sec. 25.149(f); and
(C) A speed that provides the maneuvering capability specified in
Sec. 25.143(h).
(ii) In icing conditions, VREF may not be less than:
(A) The speed determined in paragraph (b)(2)(i) of this section;
(B) 1.23 VSR0 with the landing ice accretion defined in
appendix C if that speed exceeds VREF for non-icing
conditions by more than 5 knots CAS; and
(C) A speed that provides the maneuvering capability specified in
Sec. 25.143(h) with the landing ice accretion defined in appendix C.
(3) Changes in configuration, power or thrust, and speed, must be
made in accordance with the established procedures for service
operation.
(4) The landing must be made without excessive vertical
acceleration, tendency to bounce, nose over, ground loop, porpoise, or
water loop.
(5) The landings may not require exceptional piloting skill or
alertness.
(c) For landplanes and amphibians, the landing distance on land
must be determined on a level, smooth, dry, hard-surfaced runway. In
addition--
(1) The pressures on the wheel braking systems may not exceed those
specified by the brake manufacturer;
(2) The brakes may not be used so as to cause excessive wear of
brakes or tires; and
(3) Means other than wheel brakes may be used if that means--
(i) Is safe and reliable;
(ii) Is used so that consistent results can be expected in service;
and
(iii) Is such that exceptional skill is not required to control the
airplane.
(d) For seaplanes and amphibians, the landing distance on water
must be determined on smooth water.
(e) For skiplanes, the landing distance on snow must be determined
on smooth, dry, snow.
(f) The landing distance data must include correction factors for
not more than 50 percent of the nominal wind components along the
landing path opposite to the direction of landing, and not less than
150 percent of the nominal wind components along the landing path in
the direction of landing.
(g) If any device is used that depends on the operation of any
engine, and if the landing distance would be noticeably increased when
a landing is made with that engine inoperative, the landing distance
must be determined with that engine inoperative unless the use of
compensating means will result in a landing distance not more than that
with each engine operating.
11. Amend Sec. 25.143 by revising paragraphs (c), (d), (e), (f),
and (g), and by adding new paragraphs (h), (i), and (j) to read as
follows:
Sec. 25.143 General.
* * * * *
(c) The airplane must be shown to be safely controllable and
maneuverable with the critical ice accretion appropriate to the phase
of flight defined in appendix C, and with the critical engine
inoperative and its propeller (if applicable) in the minimum drag
position:--
(1) At the minimum V2 for takeoff;
(2) During an approach and go-around; and
(3) During an approach and landing.
(d) The following table prescribes, for conventional wheel type
controls, the maximum control forces permitted during the testing
required by paragraph (a) through (c) of this section:
[[Page 67300]]
------------------------------------------------------------------------
Force, in pounds, applied to the
control wheel or rudder pedals Pitch Roll Yaw
------------------------------------------------------------------------
For short term application for 75 50 ...........
pitch and roll control--two
hands available for control.....
For short term application for 50 25 ...........
pitch and roll control--one hand
available for control...........
For short term application for ........... ........... 150
yaw control.....................
For long term application........ 10 5 20
------------------------------------------------------------------------
(e) Approved operating procedures or conventional operating
practices must be followed when demonstrating compliance with the
control force limitations for short term application that are
prescribed in paragraph (d) of this section. The airplane must be in
trim, or as near to being in trim as practical, in the preceding steady
flight condition. For the takeoff condition, the airplane must be
trimmed according to the approved operating procedures.
(f) When demonstrating compliance with the control force
limitations for long term application that are prescribed in paragraph
(d) this section, the airplane must be in trim, or as near to being in
trim as practical.
(g) When maneuvering at a constant airspeed or Mach number (up
VFC/MFC), the stick forces and the gradient of
the stick versus maneuvering load factor must lie within satisfactory
limits. The stick forces must not be so great as to make excessive
demands on the pilot's strength when maneuvering the airplane, and must
not be so low that the airplane can easily be overstressed
inadvertently. Changes of gradient that occur with changes of load
factor must not cause undue difficulty maintaining control of the
airplane, and local gradients must not be so low as to result in a
danger of overcontrolling.
(h) The maneuvering capabilities in a constant speed coordinated
turn at forward center of gravity, as specified in the following table,
must be free of stall warning or other characteristics that might
interfere with normal maneuvering:
----------------------------------------------------------------------------------------------------------------
Maneuvering
bank angle in a
Configuration Speed coordinated Thrust/power setting
turn
----------------------------------------------------------------------------------------------------------------
Takeoff................................ V2......................... 30[deg] Asymmetric WAT-
limited.\1\
Takeoff................................ V2 + XX\2\................. 40[deg] All-engines-operating
climb.\3\
En route............................... VFTO....................... 40[deg] Asymmetric WAT-
limited.\1\
Landing................................ VREF....................... 40[deg] Symmetric for -3[deg]
flight path angle.
----------------------------------------------------------------------------------------------------------------
\1\ A combination of weight, altitude, and temperature (WAT) such that the thrust or power setting produces the
minimum climb gradient specified in Sec. 25.121 for the flight condition.
\2\ Airspeed approved for all-engines-operating initial climb.
\3\ That thrust or power setting which, in the event of failure of the critical engine and without any crew
action to adjust the thrust or power of the remaining engines, would result in the thrust or power specified
for the takeoff condition at V2, or any lesser thrust or power setting that is used for all-engines-operating
initial climb procedures.
(i) When demonstrating compliance with Sec. 25.143 in icing
conditions--
(1) Controllability must be demonstrated with the ice accretion
defined in appendix C that is most critical for the particular flight
phase;
(2) It must be shown that a push force is required throughout a
pushover maneuver down to a zero g load factor, or the lowest load
factor obtainable if limited by elevator power. It must be possible to
promptly recover from the maneuver without exceeding 50 pounds pull
control force; and
(3) Any changes in force that the pilot must apply to the pitch
control to maintain speed with increasing sideslip angle must be
steadily increasing with no force reversals.
(j) For flight in icing conditions before the ice protection system
has been activated and is performing its intended function, the
following requirements apply:
(1) If activating the ice protection system depends on the pilot
seeing a specified ice accretion on a reference surface (not just the
first indication of icing), the requirements of Sec. 25.143 apply with
the ice accretion defined in appendix C, part II(e).
(2) For other means of activating the ice protection system, it
must be demonstrated in flight with the ice accretion defined in
appendix C, part II(e) that:
(i) The airplane is controllable in a pull-up maneuver up to 1.5 g
load factor; and
(ii) There is no longitudinal control force reversal during a
pushover maneuver down to 0.5 g load factor.
12. Amend Sec. 25.207 by revising paragraph (b), revising
paragraphs (e) and (f), and adding paragraphs (g) and (h) to read as
follows:
Sec. 25.207 Stall warning.
* * * * *
(b) The warning must be furnished either through the inherent
aerodynamic qualities of the airplane or by a device that will give
clearly distinguishable indications under expected conditions of
flight. However, a visual stall warning device that requires the
attention of the crew within the cockpit is not acceptable by itself.
If a warning device is used, it must provide a warning in each of the
airplane configurations prescribed in paragraph (a) of this section at
the speed prescribed in paragraphs (c) and (d) of this section. Except
for the stall warning prescribed in paragraph (h)(2)(ii) of this
section, the stall warning for flight in icing conditions prescribed in
paragraph (e) of this section must be provided by the same means as the
stall warning for flight in non-icing conditions.
(c) * * *
(d) * * *
(e) In icing conditions, the stall warning margin in straight and
turning flight must be sufficient to allow the pilot to prevent
stalling (as defined in Sec. 25.201(d)) when the pilot starts a
recovery maneuver not less than three seconds after the onset of stall
warning. When demonstrating compliance with this paragraph, the pilot
must perform the recovery maneuver in the same way as for the airplane
in non-icing conditions. Compliance with this requirement must be
demonstrated in flight with the speed reduced at rates not exceeding
one knot per second, with--
(1) The en route ice accretion defined in appendix C for the en
route configuration;
[[Page 67301]]
(2) The holding ice accretion defined in appendix C for the holding
and approach configurations;
(3) The landing ice accretion defined in appendix C for the landing
and go-around configurations; and
(4) The more critical of the takeoff ice and final takeoff ice
accretions defined in appendix C for each configuration used in the
takeoff phase of flight.
(f) The stall warning margin must be sufficient in both non-icing
and icing conditions to allow the pilot to prevent stalling when the
pilot starts a recovery maneuver not less than one second after the
onset of stall warning in slow-down turns with at least 1.5 g load
factor normal to the flight path and airspeed deceleration rates of at
least 2 knots per second. When demonstrating compliance with this
paragraph for icing conditions, the pilot must perform the recovery
maneuver in the same way as for the airplane in non-icing conditions.
Compliance with this requirement must be demonstrated in flight with--
(1) The flaps and landing gear in any normal position;
(2) The airplane trimmed for straight flight at a speed of 1.3
VSR; and
(3) The power or thrust necessary to maintain level flight at 1.3
VSR.
(g) Stall warning must also be provided in each abnormal
configuration of the high lift devices that is likely to be used in
flight following system failures (including all configurations covered
by Airplane Flight Manual procedures).
(h) For flight in icing conditions before the ice protection system
has been activated and is performing its intended function, the
following requirements apply, with the ice accretion defined in
appendix C, part II(e):
(1) If activating the ice protection system depends on the pilot
seeing a specified ice accretion on a reference surface (not just the
first indication of icing), the requirements of this section apply,
except for paragraphs (c) and (d) of this section.
(2) For other means of activating the ice protection system, the
stall warning margin in straight and turning flight must be sufficient
to allow the pilot to prevent stalling without encountering any adverse
flight characteristics when the speed is reduced at rates not exceeding
one knot per second and the pilot performs the recovery maneuver in the
same way as for flight in non-icing conditions.
(i) If stall warning is provided by the same means as for flight in
non-icing conditions, the pilot may not start the recovery maneuver
earlier than one second after the onset of stall warning.
(ii) If stall warning is provided by a different means than for
flight in non-icing conditions, the pilot may not start the recovery
maneuver earlier than 3 seconds after the onset of stall warning. Also,
compliance must be shown with Sec. 25.203 using the demonstration
prescribed by Sec. 25.201, except that the deceleration rates of Sec.
25.201(c)(2) need not be demonstrated.
13. Amend Sec. 25.237 by revising paragraph (a) to read as
follows:
Sec. 25.237 Wind velocities.
(a) For landplanes and amphibians, the following applies:
(1) A 90-degree cross component of wind velocity, demonstrated to
be safe for takeoff and landing, must be established for dry runways
and must be at least 20 knots or 0.2 VSRO, whichever is
greater, except that it need not exceed 25 knots.
(2) The crosswind component for takeoff established without ice
accretions is valid in icing conditions.
(3) The landing crosswind component must be established for:
(i) Non-icing conditions, and
(ii) Icing conditions with the landing ice accretion defined in
appendix C.
* * * * *
14. Amend Sec. 25.253 by revising paragraph (b), and adding a new
paragraph (c) to read as follows:
Sec. 25.253 High-speed characteristics.
* * * * *
(b) Maximum speed for stability characteristics. VFC/
MFC. VFC/MFC is the maximum speed at
which the requirements of Sec. Sec. 25.143(g), 25.147(e),
25.175(b)(1), 25.177, and 25.181 must be met with flaps and landing
gear retracted. Except as noted in Sec. 25.253(c), VFC/
MFC may not be less than a speed midway between
VMO/MMO and VDF/MDF, except
that for altitudes where Mach number is the limiting factor,
MFC need not exceed the Mach number at which effective speed
warning occurs.
(c) Maximum speed for stability characteristics in icing
conditions. The maximum speed for stability characteristics with the
ice accretions defined in appendix C, at which the requirements of
Sec. Sec. 25.143(g), 25.147(e), 25.175(b)(1), 25.177, and 25.181 must
be met, is the lower of:
(1) 300 knots CAS;
(2) VFC; or
(3) A speed at which it is demonstrated that the airframe will be
free of ice accretion due to the effects of increased dynamic pressure.
15. Amend Sec. 25.773 by revising paragraph (b)(1)(ii) to read as
follows:
Sec. 25.773 Pilot compartment view.
* * * * *
(b) * * *
(1) * * *
(i) * * *
(ii) The icing conditions specified in Sec. 25.1419 if
certification for flight in icing conditions is requested.
* * * * *
16. Amend Sec. 25.941 by revising paragraph (c) to read as
follows:
Sec. 25.941 Inlet, engine, and exhaust compatibility.
* * * * *
(c) In showing compliance with paragraph (b) of this section, the
pilot strength required may not exceed the limits set forth in Sec.
25.143(d), subject to the conditions set forth in paragraphs (e) and
(f) of Sec. 25.143.
17. Amend Sec. 25.1419 by revising the introductory text to read
as follows:
Sec. 25.1419 Ice protection.
If certification for flight in icing conditions is desired, the
airplane must be able to safely operate in the continuous maximum and
intermittent maximum icing conditions of appendix C. To establish
this--
* * * * *
18. Amend appendix C of part 25 by adding a new part I heading and
a new paragraph (c) to part I; and adding a new part II to read as
follows:
Appendix C of Part 25
Part I--Atmospheric Icing Conditions
(a) * * *
(c) Takeoff maximum icing. The maximum intensity of atmospheric
icing conditions for takeoff (takeoff maximum icing) is defined by the
cloud liquid water content of 0.35 g/m3, the mean effective
diameter of the cloud droplets of 20 microns, and the ambient air
temperature at ground level of minus 9 degrees Celsius (-9[deg]C). The
takeoff maximum icing conditions extend from ground level to a height
of 1,500 feet above the level of the takeoff surface.
Part II--Airframe Ice Accretions for Showing Compliance With Subpart B
(a) Ice accretions--General. Section 25.21(g) states that if
certification for flight in icing conditions is desired, the applicable
requirements of subpart B must be met in the icing conditions of
appendix C. The most critical ice accretion in terms of handling
characteristics and performance for each flight phase must be
determined, taking into consideration the atmospheric conditions of
part I of this appendix, and the flight conditions (for example,
configuration, speed, angle-of-attack,
[[Page 67302]]
and altitude). The following ice accretions must be determined:
(1) Takeoff ice is the most critical ice accretion on unprotected
surfaces, and any ice accretion on the protected surfaces appropriate
to normal ice protection system operation, occurring between liftoff
and 400 feet above the takeoff surface, assuming accretion starts at
liftoff in the takeoff maximum icing conditions of part I, paragraph
(c) of this appendix.
(2) Final takeoff ice is the most critical ice accretion on
unprotected surfaces, and any ice accretion on the protected surfaces
appropriate to normal ice protection system operation, between 400 feet
and 1,500 feet above the takeoff surface, assuming accretion starts at
liftoff in the takeoff maximum icing conditions of part I, paragraph
(c) of this appendix.
(3) En route ice is the critical ice accretion on the unprotected
surfaces, and any ice accretion on the protected surfaces appropriate
to normal ice protection system operation, during the en route phase.
(4) Holding ice is the critical ice accretion on the unprotected
surfaces, and any ice accretion on the protected surfaces appropriate
to normal ice protection system operation, during the holding flight
phase.
(5) Landing ice is the critical ice accretion on the unprotected
surfaces, and any ice accretion on the protected surfaces appropriate
to normal ice protection system operation following exit from the
holding flight phase and transition to the final landing configuration.
(6) Sandpaper ice is a thin, rough layer of ice.
(b) In order to reduce the number of ice accretions to be
considered when demonstrating compliance with the requirements of Sec.
25.21(g), any of the ice accretions defined in paragraph (a) of this
section may be used for any other flight phase if it is shown to be
more conservative than the specific ice accretion defined for that
flight phase.
(c) The ice accretion that has the most adverse effect on handling
characteristics may be used for airplane performance tests provided any
difference in performance is conservatively taken into account.
(d) Ice accretions for the takeoff phase. For both unprotected and
protected parts, the ice accretion may be determined by calculation,
assuming the takeoff maximum icing conditions defined in appendix C,
and assuming that:
(1) Airfoils, control surfaces and, if applicable, propellers are
free from frost, snow, or ice at the start of the takeoff;
(2) The ice accretion starts at liftoff;
(3) The critical ratio of thrust/power-to-weight;
(4) Failure of the critical engine occurs at VEF; and
(5) Crew activation of the ice protection system is in accordance
with a normal operating procedure provided in the Airplane Flight
Manual, except that after beginning the takeoff roll, it must be
assumed that the crew takes no action to activate the ice protection
system until the airplane is at least 400 feet above the takeoff
surface.
(e) Ice accretion before the ice protection system has been
activated and is performing its intended function. The ice accretion
before the ice protection system has been activated and is performing
its intended function is the ice accretion formed on the unprotected
and normally protected surfaces before activation and effective
operation of the ice protection system in continuous maximum
atmospheric icing conditions.
Issued in Washington, DC, on October 24, 2005.
John J. Hickey,
Director, Aircraft Certification Service.
[FR Doc. 05-21793 Filed 11-3-05; 8:45 am]
BILLING CODE 4910-13-P