[Federal Register Volume 71, Number 230 (Thursday, November 30, 2006)]
[Rules and Regulations]
[Pages 69183-69186]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E6-20275]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM321; Special Condition No. 25-338-SC]


Special Conditions: Airbus Model A380-800 Airplane, Ground 
Turning Loads

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 ground 
turning loads. These special conditions contain the additional safety 
standards that the Administrator considers necessary to

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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.

EFFECTIVE DATE: The effective date of these special conditions is 
November 9, 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 has 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 April 20, 1999, and requested that the 7-year certification period 
which had already been approved be continued. The FAA has reviewed the 
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, the special conditions would also apply to the 
other model under the provisions of 14 CFR 21.101(a)(1).

Discussion of Novel or Unusual Design Features

    The A380 has a landing gear arrangement consisting of a nose gear, 
two wing mounted gears, and two body mounted gears. This is different 
from the conventional tricycle landing gear arrangement envisioned by 
14 CFR 25.495. The simple load condition specified in Sec.  25.495, 
while providing a realistic approximation for designing a tricycle 
landing gear arrangement, will give unrealistic results for the A380. 
Safe sizing of the A380 landing gears necessitates a rational ground 
turning analysis that considers the way the airplane as a whole 
responds to a turning maneuver.
    Furthermore, recent studies of the current generation of transport 
category airplanes carried out in the U.S. and in Europe indicate a 
correlation between lower load factors in ground turns and higher gross 
weight of an airplane. This correlation was documented in the FAA-
sponsored report, DOT/FAA/AR-02/129 Side Load Factor Statistics from 
Commercial Aircraft Ground Operations, dated January 2003. As stated in 
the report's abstract, ``The results of this study clearly indicate, 
however, that the lateral loads experienced by the larger/heavier 
transport jets during ground turns are substantially less than those of 
smaller jet transports.'' Based on this rationale, for the Model A380 
airplane at maximum ramp weight--which is more than 30% heavier than 
any currently certificated airplane--the 0.5 g design turning load 
factor specified in Sec.  25.495 is conservative. A load factor of 0.45 
g is more appropriate for the A380 at maximum ramp weight. The data 
provided to the FAA support this reduced factor.
    Therefore, in lieu of the requirements of Sec.  25.495, a special 
condition regarding ground turning loads is justified for the Model 
A380 airplane. The special condition would require the applicant to 
determine the loads on the airplane during ground turning in a rational 
manner and would allow the applicant to determine a limit turning 
lateral load factor--not less than 0.45 g's--for the A380 at maximum 
ramp weight.

Discussion of Comments

    Notice of Proposed Special Conditions No. 25-05-16-SC, pertaining 
to ground turning loads for the Airbus A380 airplane, was published in 
the Federal Register on August 9, 2005 (70 FR 46106). Comments 
supporting the intent and the language of the proposed special 
conditions were received from the Airline Pilots Association (ALPA). 
Comments requesting changes were received from the Boeing Company.
    Requested change 1: Boeing states that it agrees special conditions 
are necessary, because the current regulations do not adequately 
address the A380 landing gear arrangement. However, Boeing disagrees 
with the general content of the proposed special conditions, because 
the proposed special conditions do not apply either the current safety 
standard for the Model 747 four-post gear arrangement or the standards 
for ground and loading conditions for multi-post gear arrangements 
developed by the FAA's Aviation Regulatory Advisory Committee (ARAC).
    Boeing adds that the current safety standard for a four post gear

[[Page 69185]]

arrangement is found in Special Conditions A-4 issued for the Boeing 
747 airplane and that this standard should apply to the Model A380 
``since the configurations and gear arrangements are very similar to 
the Model 747 gear arrangement.* * *'' Alternatively, Boeing suggests, 
the set of standards developed by ARAC for ground and landing 
conditions for multi-post gear arrangements should be incorporated as 
the basis of the Model A380 ground handling and landing requirements.
    FAA response: This special condition was proposed in accordance 
with 14 CFR 21.16, which states that the Administrator prescribes 
special conditions, if she or he finds that the airworthiness 
regulations do not contain adequate or appropriate safety standards for 
an aircraft because of a novel or unusual design feature. Section 21.16 
does not constrain the Administrator to prescribe only such standards 
as have been proposed by ARAC, and the Administrator routinely 
prescribes special conditions that are neither existing standards nor 
standards proposed by ARAC.
    These special conditions are motivated primarily by the size and 
weight of the Model A380 airplane and the effect of these parameters on 
ground turning loads. Nevertheless, the FAA recognizes the importance 
of the multi-post landing gear configuration on the individual landing 
gear loads. (In separate special conditions for the A380, we have 
adopted the set of standards developed by ARAC for ground and landing 
conditions for multi-post landing gear arrangements, as Boeing 
suggests. Those special conditions, No. 25-324-SC, do not address 
ground turning loads.)
    As discussed in the Notice of Proposed Special Conditions, 
pertaining to ground turning loads, the FAA concludes that, ``Safe 
sizing of the A380 landing gear necessitates a rational ground turning 
analysis that considers the way the airplane as a whole responds to a 
turning maneuver,'' and the proposed special condition contains 
provisions for such an analysis. The FAA considers these provisions to 
adequately to address the commenter's safety concern. The 747 Special 
Condition A-4 was not adopted for the A380, because it does not 
constitute a current safety standard for all four-post main landing 
gear.
    Requested change 2: Boeing states that the proposed special 
conditions are not justified by the rationale stated by the FAA in the 
Discussion of Novel or Unusual Design Features. This rationale was 
essentially that the simple load conditions specified in Sec.  25.495-
while providing a realistic approximation for designing a tricycle 
landing gear arrangement-would give unrealistic results for the A380 
and that recent studies of the current generation of transport category 
airplanes show a correlation between lower load factors in ground turns 
and higher gross weight.
    The FAA concluded that ``Based on this rationale, for the A380 at a 
maximum ramp weight--which is more than 30% heavier than any currently 
certificated airplane--the 0.5 g design turning load factor specified 
in Sec.  25.495 is conservative.'' However, the Boeing Company suggests 
that these conclusions from the operational data are broadly applicable 
to the current large/heavy fleet of transport airplanes and are not 
unique to the Model A380 configuration or design weights.
    FAA response: The FAA agrees with Boeing that conclusions from the 
recent studies are broadly applicable to the current large/heavy fleet 
and that these studies indicate that the ground turning load factor of 
Sec.  25.495 is conservative for certain heavier model airplanes. That 
conclusion does not alter the fact that an airplane of the size and 
gross weight of the A380 also exhibits decreased ground turning loads 
and thus warrants issuance of special conditions with ground turning 
loads lower than those specified in Sec.  25.495.
    Requested change 3: Boeing states that--by proposing to lower the 
side load factor in the ground turn--the proposed special conditions 
would adopt a lesser safety standard. According to the commenter,

    This is a reduction of the established standard, which will 
result in decreased gear strength relative to the existing fleet. We 
consider the current 0.5g side load factor as a 'book' case intended 
to provide relatively simple criteria to ensure adequate side 
strength in lieu of an all-inclusive rational analysis. The special 
condition does not consider supplementary criteria to maintain 
equivalence to existing safety standards.

    FAA response: As discussed above, data show that there is an 
inverse relationship between load factors experienced by airplanes in 
turns and their size and gross weight (i.e., greater weight implies 
lower load factors). Statistical analysis of these data indicates that 
the probability of achieving the ``book'' case on the A380 is 
exceedingly low--to the point that it cannot practically be achieved. 
Using a side load factor of 0.45g still results in a turning load that 
is very unlikely to be exceeded in operation. (By way of comparison, a 
single aisle airplane, such as an A320 or a Boeing 737, is more likely 
to exceed the ``book'' case of 0.5 g's in a turn than the A380 is of 
exceeding 0.45 g's.) Furthermore, the special condition states that the 
0.45g load factor may be used, only if it can be shown by rational 
analysis that this lower value cannot be exceeded in service 
considering adverse variations in airplane characteristics and 
operations. Thus there is no practical decrease in safety relative to 
that provided by Sec.  25.495. Since this special condition is based on 
a more realistic analysis, no supplementary criteria are necessary.
    Requested change 4: The commenter indicates that ``[Additionally,] 
the proposed SC would require a rational distribution of side load 
among the tires. While this provision may be conservative for the 
inboard gears, we find the SC not to be conservative for the wing 
gears. We suspect this will result in a lower level of strength for 
portions of the landing gear structure relative to the current 
commercial airplane fleet.''
    FAA response: The FAA does not agree. The special condition 
requires a rational distribution of side loads among tires in a severe 
turn, assuming a conservative turning load factor. This can be expected 
to result in side loads that are rationally distributed and 
conservative for both inboard gear and wing gear in comparison to any 
loading actually expected in operation. Boeing did not provided any 
data to support its claim that the special condition, as proposed, 
would result in a lower level of strength for portions of the landing 
gear structure relative to the current commercial fleet.
    Requested change 5: Boeing comments that ``In order to justify the 
reduced side factor, a more extensive set of likely ground maneuvers 
should be considered than those listed in the proposed special 
conditions.* * * At a minimum, regardless of the side load factor, the 
rational turning analysis should consider critical combinations of 
steering, braking, and power as well as turning in a crosswind.''
    FAA response: The FAA does not agree that to justify the reduced 
side load factor, a set of likely ground maneuvers more extensive than 
those listed should be considered in the special conditions. The 
special conditions require that the rational analysis consider ``the 
maximum load factor that can be reached during the full range of likely 
ground operations at maximum ramp weight.* * *'' The full range of 
likely ground operations would include likely critical combinations of 
steering, braking, power, and turning in crosswinds.

[[Page 69186]]

    Requested change 6: Finally, Boeing comments that ``A significant 
amount of the Model 747 main gear truck and axle assembly is designed 
by ground turn. Additionally, the axle stiffness, which is a very 
important parameter for brake interaction and for tire shoulder wear, 
could be negatively affected if the requirements are reduced. By 
lowering the loads below current practice, new service-related problems 
could result.''
    FAA response: The special conditions require the applicant to 
demonstrate that the reduced ground turning load cannot be exceeded in 
service. If the applicant can demonstrate this and can demonstrate 
compliance with other regulations affecting the integrity of landing 
gear, brakes, and tires, we consider that the potential for new 
service-related problems would be minimized. Nevertheless, as with any 
other type design, the FAA continually monitors the safety of airplanes 
in the operating fleet and has the means to require mandatory 
corrective actions, if warranted.
    Accordingly, the special conditions are adopted, as proposed, with 
a minor clarifying change to the text of subparagraph b.

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.

    The authority citation for these special conditions is as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

The Special Conditions

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the following special conditions are issued as part of 
the type certification basis for the Airbus A380-800 airplane.
    In lieu of the requirements of Sec.  25.495, the following special 
condition applies:
    a. The airplane is assumed to execute a steady turn by steering of 
any steerable gear or by application of any differential power. The 
airplane limit vertical load factor must be 1.0, and, in the absence of 
a more rational analysis, the limit airplane lateral load factor must 
be 0.5.
    b. The airplane is assumed to be in static balance, the lateral 
load factor being reacted by friction forces applied at the ground 
contact point of each tire. The lateral load must be shared between 
each individual tire in a rational or conservative manner. The 
distribution of the load among the tires must account at least for the 
effects of the factors specified in subparagraph c. (2) of this special 
condition.
    c. At maximum ramp weight, a limit value of lateral center of 
gravity (cg) inertia load factor lower than specified in subparagraph 
a. but not less than 0.45g (wing axis) may be used, if it can be shown 
by a rational analysis that this lower value cannot be exceeded. The 
rational analysis must consider at least the following:
    1. The maximum lateral load factor that can be reached during the 
full range of likely ground operations at maximum ramp weight, 
including ground turning, ``fishtailing,'' and high-speed runway exit. 
In each case, the full dynamic maneuver must be considered.
    2. The rational analysis must include at least the following 
parameters:
    (a) Landing gear spring curves and landing gear kinematics.
    (b) Reliable tire friction characteristics.
    (c) Airframe and landing gear flexibility when significant.
    (d) Airplane rigid body motion.
    (e) The worst combination of tire diameter, tire pressure, and 
runway. shapes, specified in Sec. Sec.  25.511(b)(2), 25.511(b)(3), and 
25.511(b)(4).
    d. The limit lateral load factor at maximum landing weight is 0.5.
    e. Details of the analysis and any assumptions used must be agreed 
to by the FAA. Any assumptions made in the analysis must be based on 
the intrinsic characteristics of the airplane and must be independent 
of airfield geometry. Other influences that cannot be controlled by the 
airplane design must be conservatively assessed.

    Issued in Renton, Washington, on November 9, 2006.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
 [FR Doc. E6-20275 Filed 11-29-06; 8:45 am]
BILLING CODE 4910-13-P