[Federal Register: August 21, 2006 (Volume 71, Number 161)]
[Rules and Regulations]
[Page 48453-48457]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr21au06-4]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM319; Special Conditions No. 25-321-SC]
Special Conditions: Airbus Model A380-800 Airplane,
Crashworthiness
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special conditions.
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SUMMARY: These special conditions are issued for the Airbus A380-800
airplane. This airplane will have novel or unusual design features when
compared to the state of technology envisioned in the airworthiness
standards for transport category airplanes. Many of these novel or
unusual design features are associated with the complex systems and the
configuration of the airplane, including its full-length double deck.
For these design features, the applicable airworthiness regulations do
not contain adequate or appropriate safety standards regarding crash
survivability. These special conditions contain the additional safety
standards that the Administrator considers necessary to establish a
level of safety equivalent to that established by the existing
airworthiness standards. Additional special conditions will be issued
for other novel or unusual design features of the Airbus Model A380-800
airplane.
DATES: Effective Date: The effective date for these special conditions
is July 24, 2006.
FOR FURTHER INFORMATION CONTACT: Holly Thorson, FAA, International
Branch, ANM-116, Transport Airplane Directorate, Aircraft Certification
Service, 1601 Lind Avenue, SW., Renton, Washington 98055-4056;
telephone (425) 227-1357; facsimile (425) 227-1149.
SUPPLEMENTARY INFORMATION:
Background
Airbus applied for FAA certification/validation of the
provisionally-designated Model A3XX-100 in its letter AI/L 810.0223/98,
dated August 12, 1998, to the FAA. Application for certification by the
Joint Aviation Authorities (JAA) of Europe had been made on January 16,
1998, reference AI/L 810.0019/98. In its letter to the FAA, Airbus
requested an extension to the 5-year period for type certification in
accordance with 14 CFR 21.17(c).
The request was for an extension to a 7-year period, using the date
of the initial application letter to the JAA as the reference date. The
reason given by Airbus for the request for extension is related to the
technical challenges, complexity, and the number of new and novel
features on the airplane. On November 12, 1998, the Manager, Aircraft
Engineering Division, AIR-100, granted Airbus' request for the 7-year
period, based on the date of application to the JAA.
In its letter AI/LE-A 828.0040/99 Issue 3, dated July 20, 2001,
Airbus stated that its target date for type certification of the Model
A380-800 had been moved from May 2005, to January 2006, to match the
delivery date of the first production airplane. In a subsequent letter
(AI/L 810.0223/98 issue 3, dated January 27, 2006), Airbus stated that
its target date for type certification is October 2, 2006. In
accordance with 14 CFR 21.17(d)(2), Airbus chose a new application date
of December 20, 1999, and requested that the 7-year certification
period which had already been approved be continued. The FAA has
reviewed the
[[Page 48454]]
part 25 certification basis for the Model A380-800 airplane, and no
changes are required based on the new application date.
The Model A380-800 airplane will be an all-new, four-engine jet
transport airplane with a full double-deck, two-aisle cabin. The
maximum takeoff weight will be 1.235 million pounds with a typical
three-class layout of 555 passengers.
Type Certification Basis
Under the provisions of 14 CFR 21.17, Airbus must show that the
Model A380-800 airplane meets the applicable provisions of 14 CFR part
25, as amended by Amendments 25-1 through 25-98. If the Administrator
finds that the applicable airworthiness regulations do not contain
adequate or appropriate safety standards for the Airbus A380-800
airplane because of novel or unusual design features, special
conditions are prescribed under the provisions of 14 CFR 21.16.
In addition to the applicable airworthiness regulations and special
conditions, the Airbus Model A380-800 airplane must comply with the
fuel vent and exhaust emission requirements of 14 CFR part 34 and the
noise certification requirements of 14 CFR part 36. In addition, the
FAA must issue a finding of regulatory adequacy pursuant to section 611
of Public Law 93-574, the ``Noise Control Act of 1972.''
Special conditions, as defined in 14 CFR 11.19, are issued in
accordance with 14 CFR 11.38 and become part of the type certification
basis in accordance with 14 CFR 21.17(a)(2).
Special conditions are initially applicable to the model for which
they are issued. Should the type certificate for that model be amended
later to include any other model that incorporates the same novel or
unusual design feature, or should any other model already included on
the same type certificate be modified to incorporate the same novel or
unusual design features, the special conditions would also apply to the
other model under the provisions of 14 CFR 21.101.
Discussion of Novel or Unusual Design Features
With its complex configuration, including a full-length double
deck, the Model A380 airplane has a novel and unusual design relative
to large transport category airplanes which have been previously
certificated under 14 CFR part 25. The A380 should provide a level of
crash survivability which is at least equivalent to that demonstrated
for such conventional large transport airplanes. However, its size and
configuration could cause the airplane to be subject to effects of
scale that decrease the ability of the occupants to survive a crash
landing, compared to the occupants of those conventional airplanes.
Currently, 14 CFR 25.561 contains design load conditions covering
emergency landings or minor crash landings for the local structures
which support passengers, equipment, cargo, and other large items of
mass in the passenger compartment. However, neither 14 CFR 25.561 nor
any other part 25 requirements address the structural capability of the
airframe as a whole in a crash landing. Service experience indicates
that-even without specific regulatory requirements-the airframes of
conventional transport category airplanes show reasonable structural
capability in crash landings. Therefore, in the past we have not
considered it necessary to specify design load conditions addressing
the structural capability of the airplane as a whole in a crash
landing.
The FAA, however, has no information to indicate whether an
airplane the size and configuration of the A380 would provide
reasonable airframe structural capability in a crash landing without a
specific regulatory requirement. Therefore, the FAA is proposing
special conditions which specify testing and analysis to ensure that
the Model A380 provides a level of crash survivability equivalent to
that of conventional large transport category airplanes. These special
conditions address only the vertical loading of the fuselage. The
longitudinal loading is not significantly different from that of a
conventional transport category airplane and thus is adequately
addressed by part 25.
For the special conditions, it is necessary to establish a
reference point to compare the structural capability of the A380
airplane with the structural capability of current generation airplanes
in a crash. This reference point is referred to as the ``Limit of
Reasonable Survivability.'' It is defined--in terms of the vertical
descent rate--as the level of structural degradation that would lead,
either directly or by exceedance of physiological limits of the
occupants, to a significant reduction in the probability of survival in
an otherwise survivable incident. (An incident can be unsurvivable due
to a non-structural cause, such as a fire. An otherwise survivable
incident, then, is one in which no fire or other cause makes the
incident unsurvivable.) We intend that this Limit of Reasonable
Survivability be determined first for the current generation of the
applicant's airplanes and then for the A380 to show that the latter has
equal or better characteristics at the same vertical descent rate.
The special conditions contain a provision to ensure that the
supporting airframe structure is strong and rigid enough to provide
survivable living space and to hold seats, overhead bins, and other
items of mass in place, even if the local attachment hardware is
designed to exceed the minimum strength required by Sec. 25.561. To
provide this protection, the special conditions specify that the
airframe structure must be able to support the loads imposed by items
of mass, assuming that their local supporting structure does not fail,
thus relieving the load on the supporting airframe structure. This
assumption will ensure that the airframe structure will not collapse,
even if the strength of the local attachment for items of mass exceeds
the strength required by Sec. 25.561. Since it is the airframe as a
whole and its survivable living space that are the subject of these
special conditions, the FAA does not intend to increase the strength
requirements of Sec. 25.561 by special condition. Therefore, the
special conditions state explicitly that the attachments of items of
mass need not be designed for static emergency landing loads in excess
of those specified in Sec. 25.561.
Since larger airframe structures typically have more volume within
which to absorb energy, they normally provide occupants with reasonable
protection from crash loads. Therefore, the effects of the A380 design
on occupant loads are not expected to be significant. In order to
confirm that this assumption is correct, these special conditions
require an assessment of the effect of the design on the occupant
loads. For the purposes of these special conditions, an analytical tool
known as the Dynamic Response Index (DRI) is used to make the
assessment. The DRI was developed through research and is documented in
USAA VSCOM TR 89-D-22B, ``Aircraft Crash Survival Design Guide, Volume
II, Aircraft Design Crash Impact Conditions and Human Tolerance.'' The
DRI approximates the effect of an impact on spinal load. Based on the
results of the assessment using DRI, any additional, detailed occupant
load considerations can be established.
Discussion of Comments
Notice of Proposed Special Conditions No. 25-05-14-SC, pertaining
to crashworthiness requirements for the Airbus A380 airplane, was
published in the Federal
[[Page 48455]]
Register on August 9, 2005 (70 FR 46102). Comments were received from
the Airline Pilots Association (ALPA), the Association of Flight
Attendants (AFA), and the Boeing Company.
Requested change 1: ALPA addresses the first sentence in Section b.
of the special conditions which specifies that, ``The occupants will be
protected from the release of seats, overhead bins, and other items of
mass due to structural deformation of the supporting structure * * *
.''
ALPA states,
``Unless there is a procedure/system in place in revenue service
that prevents the seat and bin from being loaded in excess of their
rated limit, seats and bins under the requirements of Section b. must
be tested within the full range of likely loads, not simply up to their
rated limit. Overhead bins are notorious for failing in crash scenarios
where the remainder of the cabin remains intact. In addition, the seat
requirements for testing with only a 50th percentile male should be
reconsidered to evaluate the full range of occupants, or at least the
5th to 95th percentile of humans.''
FAA response: Accommodating the changes requested by ALPA would be
beyond the scope of this rulemaking. The purpose of the special
condition is to assure that the large size and full length double deck
configuration of the A380 design do not degrade the survivability
characteristics of the A380 fuselage shell compared to designs for
conventional large transport category airplanes. The purpose is not to
create a higher safety standard for the A380.
To accomplish a proper comparison, the mass of items and the weight
of passengers are defined in the same way as they would be for
conventional airplane designs. Overhead bins are required to be
evaluated for the rated bin load, and seats are required to be
evaluated for the mass of a 50th percentile male occupant. To adopt a
procedure to prevent a seat or bin from being loaded in excess of its
rated design or to adopt a higher passenger weight for the evaluation
of seat strength would represent a difference from the certification
criteria used for conventional large transport category airplane
designs.
Since the A380 is not unique or unusual with regard to these
certification criteria, the requested changes are considered to be
beyond the scope of this rulemaking. Accordingly, we have made no
changes to the special conditions, as proposed.
Requested change 2: AFA recommends deleting Section c. of the
special condition and all reference to use of the DRI as a measure of
``physiological limits'' of a crash. Instead, AFA suggests relying on
Sections a., b., and d. for demonstrations of survivability.
AFA supports its recommendation with a detailed analysis of the
development and use of the DRI and reaches the following conclusion:
``The DRI is useful, preferably with other criteria, to predict
minor to moderate injury in ejection seats with occupants who are
well restrained in the vertically seated posture, and possibly in
crashes. The DRI has never shown the ability to predict survival (or
anything else) in a crash that could cause severe but not fatal
injury.''
FAA response: The DRI is being used as a metric to compare the
occupant dynamic response in the Model A380 with that in other airplane
designs; it is not being used as a criterion of injury. Section c. of
the special condition states that the ``Dynamic Response Index
experienced by the occupants will be no more severe than that
experienced on conventional large transport airplanes.'' This
comparison does not involve establishing an injury criterion for DRI.
The FAA considers the DRI to be an appropriate metric for the
comparative analysis required by the special condition. Since it is
only the vertical loading that is simulated in the analysis, the one
degree of freedom spring-mass model on which DRI is based is acceptable
to the FAA. Accordingly, no change has been made to Section c. of the
special condition, as proposed.
Requested change 3: AFA states, ``The proposed special condition[s]
envision a simple vertical impact as the environment to compare the
crashworthiness of the A380-800 airplane with that of `conventional
large transport airplanes.' The `conventional large transport airplane'
is not specifically designated.'' \1\ AFA suggests that a simple
vertical crash impact is insufficient to judge crashworthiness and
recommends that, ``The impact conditions in the Special Conditions
should reflect a representative crash environment that includes at
least both vertical and longitudinal components. The conditions used in
the Jamshidiat study (op. cit.) would be appropriate.'' According to
AFA, the impact conditions studied by Jamshidiat et al. were much more
realistic and severe than the simple vertical impact proposed by the
special condition.
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\1\ Airbus compared construction of the very large A380 to that
of the ``conventional large'' A320 and A340 both of which are
currently in production.
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AFA also discusses the Department of Defense (DOD) Crash Protection
Handbook, which summarizes critical findings of past crashworthiness
studies. One of those findings is of particular concern for the A380-
800 aircraft:
``For larger aircraft, the earth-scooping criteria associated
with the low angle impact of Mil-Std-1290 were shown to be
impractical. This conclusion was based on the fact that the
requirement, which was based on G loading, would impose a severe
weight penalty on large airframes (over approximately 20,000
pounds). The criteria described in Mil-Std-1290 were that, `The nose
section shall be designed to preclude any earth plowing and scooping
tendency when the forward 25 percent of the fuselage has a uniformly
applied local upward load of 10g and a rearward load of 4g or the
ditching loads of Mil-A-8865A, whichever is the greatest.' ''
AFA states, ``Because of its size, it is doubtful if the A380-800
provides adequate protection against earth scooping. Earth scooping can
disrupt the continuity of the bottom of the aircraft (e.g., the British
Midlands 737 crash) and result in severe compromise of living space,
and thus of survivability. It must be considered in any evaluation of
crashworthiness.''
FAA response: The FAA agrees that a simple vertical crash impact is
insufficient to judge overall crashworthiness, because (1) there is no
agreed standard to judge an acceptable level of crashworthiness, and
(2) the behavior of airplanes during minor crashes is highly complex
and variable. However, that does not mean that meaningful
crashworthiness evaluations cannot be made by isolating certain
airplane characteristics that contribute to post crash survival, such
as the ability of a fuselage to withstand crushing or collapse due to
the vertical forces resulting from impact with the ground. This is the
effect addressed by the A380 special condition.
While there are many factors that may influence the survivability
of the fuselage, the FAA considers the ability of a fuselage to survive
a vertical drop without crushing or collapse to be a major factor. In
fact, the FAA has conducted vertical drop testing of actual fuselage
sections for this very purpose, that is, to determine how current
generation fuselages perform in a minor crash landing and to identify
design features that affect their performance.
The demonstration required by this special condition is intended to
show whether the A380, including the full length upper deck, is able to
resist crushing or floor collapse in a vertical drop as well as other
conventional large transport airplanes. The requirement to conduct this
demonstration does not establish a higher level of safety for the A380.
In terms of vertical descent rate,
[[Page 48456]]
it provides for equivalence to the performance of existing large
transport airplanes.
The FAA does not agree with AFA that the A380 analysis was overly
unrealistic or has little value, compared to the study performed by
Jamshidiat et al. The Jamshidiat study was performed for a different
reason than this A380 special condition. Its purpose was to assess the
effect of airplane size on the longitudinal and transverse acceleration
loads experienced by occupants. The A380 special condition addresses
the strength of the fuselage shell and its ability to avoid crushing
due to vertical impact loading. The Jamshidiat study modeled the
fuselage characteristics that are relevant for evaluating the
longitudinal and transverse acceleration loads experienced by
occupants. The A380 special condition addresses the characteristics of
the fuselage construction that are relevant to its ability to avoid
crushing. Therefore, the A380 special condition and the Jamshidiat
study are complementary. In fact, the results of the Jamshidiat study
support our assumption that the Sec. 25.561 longitudinal accelerations
are adequate for design of the A380 and, therefore, do not need to be
addressed in the A380 special condition.
Finally, the FAA does not agree that the DOD crash handbook
discussion of earth plowing/scooping indicates that it is doubtful that
the A380-800 provides adequate protection against earth scooping. The
comparison the DOD drew between large airplanes and small was between
737-size airplanes (typically greater than 140,000 pounds gross weight)
and business jet or trainer size airplanes (typically smaller than
20,000 pounds gross weight), not between 737-size airplanes and A380-
size airplanes (over 900,000 pounds gross weight).
We do not believe that any evidence indicates that the earth
plowing/scooping behavior of an A380-size airplane will be more severe
than for a 747-size airplane. In fact, a conclusion of the Jamshidiat
report cited by AFA indicates that the opposite is probably true:
``The longitudinal crash deceleration was a function of the
impact slope, the condition of the impact surface, the nature of
obstacles and the relative radius of curvature of the fuselage cross
section and the nose plan-form. The 747-400, with its larger radii
of curvature and greater energy absorption of the lower fuselage
structure has an inherent advantage over the 737-400 because
obstacles do not follow scaling rules.''
The FAA agrees with this reasoning and by extension concludes that
the A380 will have an inherent advantage over the 747 and can be
expected to produce lower longitudinal crash decelerations because of
its size.
Requested change 4: The Boeing Company suggests that the proposed
special conditions be revised or withdrawn, stating the following:
``A requirement to show equivalency to an existing airplane is
unprecedented and beyond the scope provided for by FAR 21.16 for
Special Conditions. [Section] 21.16 allows special conditions to be
issued `to establish a level of safety equivalent to that
established in the regulations.' It does not allow the FAA to issue
special conditions to achieve a level of safety inherent in a past
product design * * * ''
``Existing Part 25 regulations already provide for the
structural integrity and crashworthiness of the passenger cabin. To
require the determination and comparison to other aircraft for the
`Limit of Reasonable Survivability' should be addressed with general
rulemaking, as it is a general upgrade of the requirements that
should apply to all aircraft types * * *. Since Part 25 already
contains passenger static and dynamic survivability requirements,
the upgrading of those requirements must come through general
rulemaking and not special conditions.''
FAA response: The FAA does not agree with the commenter that this
special condition is beyond the scope provided for by 14 CFR 21.16.
That section states that
``If the Administrator finds that the airworthiness regulations
of this subchapter do not contain adequate or appropriate safety
standards for an aircraft * * * because of a novel or unusual design
feature of the aircraft * * * he prescribes special conditions and
amendments thereto for the product. The special conditions * * *
contain such safety standards for the aircraft * * * as the
Administrator finds necessary to establish a level of safety
equivalent to that established in the regulations.''
The level of safety established in the part 25 regulations for
transport category airplanes is evidenced by the safety record
demonstrated in service by airplanes so certificated. Although an
overall airframe crashworthiness requirement has never been the subject
of a part 25 regulation, current generation airplanes certificated
under part 25 have exhibited a level of crashworthiness that the FAA
considers to be adequate. These airplanes include those with a single
deck and Boeing Model 747 with an upper deck which is considerably
smaller (in both length and width) than that of the A380. The current
part 25 regulations have no doubt contributed to this level of safety,
even though no specific regulation has addressed the performance of the
airframe in a crash landing, because the regulations have determined
the airframe strength, which service experience has shown to be
adequate.
The relevant novel or unusual design features of the A380 vis-
[agrave]-vis airframe crashworthiness are its size, gross weight, and
full length double deck configuration, which are without precedent in
the current commercial transport airplane fleet. This special condition
requires a demonstration that the A380 provides a level of crash
survivability equivalent to that of conventional large transport
airplanes. Therefore, the FAA does not agree with the Boeing Company
that this special condition is beyond the scope provided for by Sec.
21.16.
Further, the FAA does not agree that the part 25 regulations
already provide for the structural integrity and crashworthiness of the
passenger cabin for the Airbus A380. The existing regulations address
the seats, restraint of passengers, equipment, cargo and other large
masses contained in the passenger cabin and their attachment to the
airframe, so as to avoid failure of structure which would release these
items in the cabin during a minor crash landing and cause injury or
block emergency escape routes. They do not, however, address the
crashworthiness of fuselage structure as a whole and its ability to
avoid collapse in a minor crash landing.
Finally, the FAA does not consider it necessary to address other
airplane designs with general rulemaking. It is the unique
characteristics of the A380 that motivates this special condition. No
other transport airplane is as large or heavy as the A380 or has a full
length double deck, and, therefore, there is no need for general
rulemaking.
Applicability
As discussed above, these special conditions are applicable to the
Airbus A380-800 airplane. Should Airbus apply at a later date for a
change to the type certificate to include another model incorporating
the same novel or unusual design features, these special conditions
would apply to that model as well under the provisions of Sec. 21.101.
Conclusion
This action affects only certain novel or unusual design features
of the Airbus A380-800 airplane. It is not a rule of general
applicability.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
0
The authority citation for these special conditions is as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.
[[Page 48457]]
The Special Conditions
0
Accordingly, pursuant to the authority delegated to me by the
Administrator, the following special condition is issued as part of the
type certification basis for the Airbus A380-800 airplane.
In addition to the requirements of Sec. Sec. 25.561, 25.562,
25.721, and 25.785, the following special condition applies:
It must be demonstrated that the Model A380 provides a level of
crash survivability equivalent to that of conventional large transport
airplanes. This may be achieved by demonstrating by test or validated
analysis that--at impacts up to a vertical descent rate representing
the Limit of Reasonable Survivability--the structural capability of
typical fuselage sections is equal to or better than that of a
conventional large transport airplane. (The Limit of Reasonable
Survivability is defined as the level of structural degradation that
would either directly or by exceedance of physiological limits of the
occupants lead to a significant reduction in the probability of
survival in an otherwise survivable incident.) The results of this
demonstration must show the following:
a. Structural deformation will not result in infringement of the
occupants' normal living space.
b. The occupants will be protected from the release of seats,
overhead bins, and other items of mass due to structural deformation of
the supporting structure. That is, the supporting structure must be
able to support the loads imposed by these items of mass, assuming that
they remain attached during the impact event, and the floor structure
must deform in a way that would allow them to remain attached. However,
the attachments of these items need not be designed for static
emergency landing loads in excess of those specified in Sec. 25.561.
c. The Dynamic Response Index experienced by the occupants will not
be more severe than that experienced on conventional large transport
airplanes. (The Dynamic Response Index is described in USAA VSCOM TR
89-D-22B, ``Aircraft Crash Survival Design Guide, Volume II, Aircraft
Design Crash Impact Conditions and Human Tolerance.'')
d. Cargo loading of the fuselage for this evaluation accounts for
variations that could have a deleterious effect on structural
performance.
Issued in Renton, Washington, on July 24, 2006.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. E6-13796 Filed 8-18-06; 8:45 am]
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