[Federal Register: November 13, 2003 (Volume 68, Number 219)]
[Proposed Rules]
[Page 64283-64286]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr13no03-8]
-----------------------------------------------------------------------
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 2001-NM-366-AD]
RIN 2120-AA64
Airworthiness Directives; Learjet Model 31, 31A, 35, 35A (C-21A),
36, and 36A Airplanes
AGENCY: Federal Aviation Administration, DOT.
ACTION: Notice of proposed rulemaking (NPRM).
-----------------------------------------------------------------------
SUMMARY: This document proposes the adoption of a new airworthiness
directive (AD) that is applicable to certain Learjet Model 31, 31A, 35,
35A (C-21A), 36, and 36A airplanes. This proposal would require
modification of the drag angles of the fuselage and engine pylons to
gain access to the shear webs of the forward engine beams; repetitive
inspections of the shear webs of the forward engine beams for cracks;
follow-on actions; and modification/repair of the shear webs of the
forward engine beams, as necessary, which would terminate the
repetitive inspections. This action is necessary to prevent significant
structural damage to the engine pylons, possible separation of the
engines from the fuselage, and consequent reduced controllability of
the airplane. This action is intended to address the identified unsafe
condition.
DATES: Comments must be received by December 29, 2003.
ADDRESSES: Submit comments in triplicate to the Federal Aviation
Administration (FAA), Transport Airplane Directorate, ANM-114,
Attention: Rules Docket No. 2001-NM-366-AD, 1601 Lind Avenue, SW.,
Renton, Washington 98055-4056. Comments may be inspected at this
location between 9 a.m. and 3 p.m., Monday through Friday, except
Federal holidays. Comments may be submitted via fax to (425) 227-1232.
Comments may also be sent via the Internet using the following address: 9-anm-nprmcomment@faa.gov. Comments sent via fax or the Internet must
contain ``Docket No. 2001-NM-366-AD'' in the subject line and need not
be submitted in triplicate. Comments sent via the Internet as attached
electronic files must be formatted in Microsoft Word 97 or 2000 or
ASCII text.
The service information referenced in the proposed rule may be
obtained from Learjet, Inc., One Learjet Way, Wichita, Kansas 67209-
2942. This information may be examined at the FAA, Transport Airplane
Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA,
Wichita Aircraft Certification Office, 1801 Airport Road, Room 100,
Mid-Continent Airport, Wichita, Kansas.
FOR FURTHER INFORMATION CONTACT: Steven Litke, Aerospace Engineer,
Airframe Branch, ACE-118W, FAA, Wichita Aircraft Certification Office,
1801 Airport Road, Room 100, Mid-Continent Airport, Wichita, Kansas
67209; telephone (316) 946-4127; fax (316) 946-4107.
SUPPLEMENTARY INFORMATION:
[[Page 64284]]
Comments Invited
Interested persons are invited to participate in the making of the
proposed rule by submitting such written data, views, or arguments as
they may desire. Communications shall identify the Rules Docket number
and be submitted in triplicate to the address specified above. All
communications received on or before the closing date for comments,
specified above, will be considered before taking action on the
proposed rule. The proposals contained in this action may be changed in
light of the comments received.
Submit comments using the following format:
[sbull] Organize comments issue-by-issue. For example, discuss a
request to change the compliance time and a request to change the
service bulletin reference as two separate issues.
[sbull] For each issue, state what specific change to the proposed
AD is being requested.
[sbull] Include justification (e.g., reasons or data) for each
request.
Comments are specifically invited on the overall regulatory,
economic, environmental, and energy aspects of the proposed rule. All
comments submitted will be available, both before and after the closing
date for comments, in the Rules Docket for examination by interested
persons. A report summarizing each FAA-public contact concerned with
the substance of this proposal will be filed in the Rules Docket.
Commenters wishing the FAA to acknowledge receipt of their comments
submitted in response to this action must submit a self-addressed,
stamped postcard on which the following statement is made: ``Comments
to Docket Number 2001-NM-366-AD.'' The postcard will be date stamped
and returned to the commenter.
Availability of NPRMs
Any person may obtain a copy of this NPRM by submitting a request
to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules
Docket No. 2001-NM-366-AD, 1601 Lind Avenue, SW., Renton, Washington
98055-4056.
Discussion
The FAA has received reports that cracks in the shear webs of the
forward engine beams were discovered on certain Learjet Model 31, 31A,
35, 35A (C-21A), 36, and 36A airplanes, which experienced damage while
landing. Further investigation revealed that the cracks were caused by
repetitive loading of the engine beams during airplane operation (i.e.,
flight, maneuver, taxi, and landing). The engine beams are the primary
structural elements of the pylon support for each engine. Such
cracking, if not corrected, could result in significant structural
damage to the engine pylons, possible separation of the engines from
the fuselage, and consequent reduced controllability of the airplane.
Explanation of Relevant Service Information
We have reviewed and approved Bombardier Service Bulletin 31-51-2
(for Model 31 airplanes) and Bombardier Service Bulletin 35/36-51-3
(for Model 35 and 36 airplanes); both dated February 1, 2001. These
service bulletins include procedures for modifying the drag angles of
the fuselage and engine pylons to gain access to the shear webs of the
forward engine beams. The modification includes including removing the
upper forward drag angles, trimming the slots in the fuselage and pylon
skins, creating slots in the drag angles to match slots in the fuselage
and pylon skins, grit blasting the radius of the engine shear webs, re-
identifying the drag angles, installing new nutplates on the pylon
skins, re-installing the upper forward drag angles, fillet sealing the
drag angles to the fuselage and engine pylon skins, installing covers
on the drag angles, fay surfacing the covers to the drag angles, and
fillet sealing the cover edges.
The service bulletins also include procedures for repetitive
detailed inspections (using a probe) and general visual inspections of
the shear webs of the forward engine beams for cracking. The probe
inspection includes grit blasting areas of the shear webs of the
forward engine beams, calibrating a micro-ohmmeter, attaching a test
probe to the micro-ohmmeter, applying the test probe to the base of the
forward and aft shear webs, applying the test probe to the radius of
the forward and aft shear webs, inspecting the forward and aft shear
webs for visible cracks, applying primer to the grit blasted areas of
the shear webs of the forward engine beam, and determining if the
resistance values of the probe inspection are within the acceptable
limits specified in the service bulletins.
We have also reviewed and approved Bombardier Service Bulletin 31-
51-3, Revision 1 (for Model 31 airplanes) and Bombardier Service
Bulletin 35/36-51-4, Revision 1 (for Model 35 and 36 airplanes), both
dated August 2, 2001. These service bulletins describe procedures for
modifying/repairing the shear webs of the forward engine beams. The
modification/repair procedures include trimming the upper and lower
flanges of frame 24, measuring the lengths and dimensions of existing
cracks in the shear webs of the forward engine beams and reporting the
results to the manufacturer, installing the appropriate parts kits,
fabricating certain parts, and installing new hardware and a jumper on
the conduit located between stringers 6 and 7 on the left side of the
airplane. Modification/repair of the shear webs eliminates the need for
the repetitive detailed inspections (using a probe) and general visual
inspections of the shear webs of the forward engine beams for cracking.
Accomplishment of the actions specified in these service bulletins
is intended to adequately address the identified unsafe condition.
Explanation of Requirements of Proposed Rule
Since an unsafe condition has been identified that is likely to
exist or develop on other products of this same type design, the
proposed AD would require accomplishment of the actions specified in
the service bulletins described previously, except as discussed under
``Differences Between the Proposed Rule and the Service Bulletins.''
Flight With Cracks
Operators should note that, while it is not the FAA's normal policy
to allow flight with known cracks, this proposed AD does permit further
flight with cracking within certain limits. If the crack size limits
are strictly observed and if repetitive inspections are performed at
the required intervals, cracks that grow beyond the limits will be
detected, and corrective action taken, before they can grow to a size
that would create an unacceptable risk of structural failure.
This proposed AD allows flight with crack openings less than 0.03
inch, provided that (1) the crack is not part of multi-site damage, (2)
the crack growth is easily detectable, and (3) the established
inspection procedures would detect cracked structure at intervals that
would permit repairs to be accomplished before the structure's strength
falls below ultimate load carrying capability.
Differences Between the Proposed Rule and the Service Bulletins
Although the service bulletins either do not reference repair
instructions or specify that operators may contact the manufacturer for
disposition of certain repair conditions, this proposed AD would
require operators to repair those conditions per a method approved by
the FAA.
[[Page 64285]]
The service bulletins also specify to submit information to the
manufacturer; however, this proposed AD does not include such a
requirement.
Clarification of Compliance Times
The follow-on actions and compliance times for the general visual
inspection required by paragraph (a) of this AD are not clearly stated
in the service bulletins. We have specified the compliance time and
follow-on actions in paragraph (d) of this proposed AD.
Cost Impact
There are approximately 893 airplanes of the affected design in the
worldwide fleet. The FAA estimates that 673 airplanes of U.S. registry
would be affected by this proposed AD.
It would take between 2 and 3 work hours per airplane to accomplish
the proposed modification, at an average labor rate of $65 per work
hour. Required parts would cost approximately $243 per airplane. Based
on these figures, the cost impact of the proposed modification on U.S.
operators is estimated to be between $251,029 and $294,774, or between
$373 and $438 per airplane.
We estimate that it would take 3 work hours to perform the proposed
inspection, and that the average labor rate is $65 per work hour. Based
on this figure, the cost impact of the proposed inspections on U.S.
operators is estimated to be $131,235, or $195 per airplane, per
inspection cycle.
The cost impact figures discussed above are based on assumptions
that no operator has yet accomplished any of the proposed requirements
of this AD action, and that no operator would accomplish those actions
in the future if this proposed AD were not adopted. The cost impact
figures discussed in AD rulemaking actions represent only the time
necessary to perform the specific actions actually required by the AD.
These figures typically do not include incidental costs, such as the
time required to gain access and close up, planning time, or time
necessitated by other administrative actions. The manufacturer may
cover the cost of replacement parts associated with this proposed AD,
subject to warranty conditions. Manufacturer warranty remedies may also
be available for labor costs associated with this proposed AD. As a
result, the costs attributable to the proposed AD may be less than
stated above.
Regulatory Impact
The regulations proposed herein 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. Therefore, it
is determined that this proposal would not have federalism implications
under Executive Order 13132.
For the reasons discussed above, I certify that this proposed
regulation (1) is not a ``significant regulatory action'' under
Executive Order 12866; (2) is not a ``significant rule'' under the DOT
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979);
and (3) if promulgated, will not have a significant economic impact,
positive or negative, on a substantial number of small entities under
the criteria of the Regulatory Flexibility Act. A copy of the draft
regulatory evaluation prepared for this action is contained in the
Rules Docket. A copy of it may be obtained by contacting the Rules
Docket at the location provided under the caption ADDRESSES.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Safety.
The Proposed Amendment
Accordingly, pursuant to the authority delegated to me by the
Administrator, the Federal Aviation Administration proposes to amend
part 39 of the Federal Aviation Regulations (14 CFR part 39) as
follows:
PART 39--AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
2. Section 39.13 is amended by adding the following new
airworthiness directive:
Learjet: Docket 2001-NM-366-AD.
Applicability: The following airplanes, certificated in any
category, as applicable:
Table 1.--Applicability
----------------------------------------------------------------------------------------------------------------
Model As listed in Bombardier service bulletin
----------------------------------------------------------------------------------------------------------------
31 and 31A Airplanes................... 31-51-2, dated February 1, 2001; and 31-51-3, Revision 1, dated August
2, 2001.
35, 35A (C-21A), 36 and 36A Airplanes.. 35/36-51-3, dated February 1, 2001; and 35/36-51-4, Revision 1, dated
August 2, 2001.
----------------------------------------------------------------------------------------------------------------
Compliance: Required as indicated, unless accomplished
previously.
To prevent significant structural damage to the engine pylons,
possible separation of the engines from the fuselage, and consequent
reduced controllability of the airplane, accomplish the following:
Inspections
(a) At the later of the times specified in paragraphs (a)(1) and
(a)(2) of this AD: Do a detailed inspection (using a probe) and a
general visual inspection of the shear webs of the forward engine
beams (including modification of the drag angles) for cracking in
accordance with the Accomplishment Instructions of Bombardier
Service Bulletin 31-51-2 (for Model 31 airplanes) or 35/36-51-3 (for
Model 35 and 36 airplanes), both dated February 1, 2001; as
applicable.
(1) Prior to the accumulation of 3,000 total flight hours; or
(2) Within 1,200 flight hours or 1 year after the effective date
of this AD, whichever occurs first.
Note 1: For the purposes of this AD, a general visual inspection
is defined as: ``A visual examination of an interior or exterior
area, installation, or assembly to detect obvious damage, failure,
or irregularity. This level of inspection is made from within
touching distance unless otherwise specified. A mirror may be
necessary to enhance visual access to all exposed surfaces in the
inspection area. This level of inspection is made under normally
available lighting conditions such as daylight, hangar lighting,
flashlight, or droplight and may require removal or opening of
access panels or doors. Stands, ladders, or platforms may be
required to gain proximity to the area being checked.''
Note 2: For the purposes of this AD, a detailed inspection is
defined as: ``An intensive visual examination of a specific
structural area, system, installation, or assembly to detect damage,
failure, or irregularity. Available lighting is normally
supplemented with a direct source of good lighting at intensity
deemed appropriate by the inspector. Inspection aids such as mirror,
magnifying lenses, etc., may be used. Surface cleaning and elaborate
access procedures may be required.''
Detailed Probe Inspection Follow-on Actions
(b) Following the detailed probe inspection required by
paragraph (a) of this AD, do the follow-on actions specified in
paragraphs (b)(1), (b)(2), or (b)(3) of this AD, as
[[Page 64286]]
applicable, in accordance with the Accomplishment Instructions of
Bombardier Service Bulletin 31-51-2 or 35/36-51-3, both dated
February 1, 2001; as applicable.
(1) If the resistance measured during the inspection is less
than 0.110 milliohm: Repeat the inspections required by paragraph
(a) of this AD thereafter at intervals not to exceed 1,200 flight
hours.
(2) If the resistance measured during the inspection is 0.110
milliohm or more, but less than 0.150 milliohm: Within the next
1,200 flight hours, repair and modify the forward engine beam shear
web in accordance with the Accomplishment Instructions of Bombardier
Service Bulletin 31-51-3, Revision 1 (for Model 31 airplanes) or 35/
36-51-4, Revision 1 (for Model 35 and 36 airplanes), both dated
August 2, 2001; as applicable.
(3) If the resistance measured during the inspection is 0.150
milliohm or more: Before further flight, repair and modify the
forward engine beam shear web in accordance with the Accomplishment
Instructions of Bombardier Service Bulletin 31-51-3, Revision 1, or
35/36-51-4, Revision 1; as applicable.
General Visual Inspection Follow-On Actions
(c) Following the general visual inspection required by
paragraph (a) of this AD, do all of the applicable follow-on actions
at the times specified in the Accomplishment Instructions of
Bombardier Service Bulletin 31-51-2 or 35/36-51-3, both dated
February 1, 2001; as applicable; except as specified in paragraph
(d) of this AD.
(d) If any crack opening is found that is more than 0.03 inch
during the general visual inspection required by paragraph (a) of
this AD: Before further flight, do the actions specified in
paragraphs 2.C.(16)(a) and 2.C.(16)(b) of Bombardier Service
Bulletin 31-51-2 or 35/36-51-3, both dated February 1, 2001; as
applicable; repair per a method approved by the Manager, Wichita
Aircraft Certification Office (ACO), FAA; and do the terminating
action specified in paragraph (e) of this AD.
Terminating Action
(e) Modification of the shear webs by accomplishing all of the
actions specified in the Accomplishment Instructions of Bombardier
Service Bulletin 31-51-3, Revision 1, or 35/36-51-4, Revision 1,
both dated August 2, 2001; as applicable; terminates the initial
inspections required by paragraph (a) and the repetitive inspections
required by paragraph (b)(1) of this AD.
Repair Approval
(f) Where any service bulletin identified in this AD specifies
that the manufacturer may be contacted for disposition of certain
repair conditions, repair per a method approved by the Manager,
Wichita ACO, FAA.
Submission of Inspection Results Not Required
(g) Although the service bulletins identified in this AD specify
to submit information to the manufacturer, this AD does not include
such a requirement.
Alternative Methods of Compliance
(h) In accordance with 14 CFR 39.19, the Manager, Wichita ACO,
is authorized to approve alternative methods of compliance for this
AD.
Issued in Renton, Washington, on November 6, 2003.
Ali Bahrami,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 03-28399 Filed 11-12-03; 8:45 am]
BILLING CODE 4910-13-P