[Federal Register Volume 74, Number 194 (Thursday, October 8, 2009)]
[Rules and Regulations]
[Pages 51759-51761]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E9-24339]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM403; Special Conditions No. 25-385-SC]


Special Conditions: Boeing Model 747-8/-8F Airplanes, Structural 
Design Requirements for Four-Post Main Landing Gear System

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Boeing Model 747-
8/-8F airplane. This airplane will have novel or unusual design 
features associated with a four-post main landing gear system. The 
applicable airworthiness regulations do not contain adequate or 
appropriate safety standards for this design feature. 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.

DATES: Effective Date: November 9, 2009.

FOR FURTHER INFORMATION CONTACT: Mark Freisthler, FAA, Airframe & Cabin 
Safety Branch, ANM-115, Transport Airplane Directorate, Aircraft 
Certification Service, 1601 Lind Avenue, SW., Renton, Washington 98057-
3356; telephone (425) 227-1119; facsimile (425) 227-1149.

SUPPLEMENTARY INFORMATION: 

Background

    On November 4, 2005, The Boeing Company, P.O. Box 3707, Seattle, WA 
98124, applied for an amendment to Type Certificate Number A20WE to 
include the new Model 747-8 passenger airplane and the new Model 747-8F 
freighter airplane. The Model 747-8 and the Model 747-8F are 
derivatives of the 747-400 and the 747-400F, respectively. Both the 
Model 747-8 and the Model 747-8F are four-engine jet transport 
airplanes that will have a maximum takeoff weight of 970,000 pounds and 
new General Electric GEnx-2B67 engines. The Model 747-8 will have two 
flight crew and the capacity to carry 660 passengers. The Model 747-8F 
will have two flight crew and a zero passenger capacity, although 
Boeing has submitted a petition for exemption to allow the carriage of 
supernumeraries.

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Boeing must show that the 
Model 747-8 and 747-8F (hereafter referred as 747-8/-8F) meet the 
applicable provisions of part 25, as amended by Amendments 25-1 through 
25-117, except for earlier amendments as agreed upon by the FAA. These 
regulations will be incorporated into Type Certificate No. A20WE after 
type certification approval of the 747-8/-8F.
    In addition, the certification basis includes other regulations, 
special conditions and exemptions that are not relevant to these 
special conditions. Type Certificate No. A20WE will be updated to 
include a complete description of the certification basis for these 
model airplanes.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., 14 CFR part 25) do not contain adequate or 
appropriate safety standards for the 747-8/-8F because of a novel or

[[Page 51760]]

unusual design feature, special conditions are prescribed under the 
provisions of Sec.  21.16.
    In addition to the applicable airworthiness regulations and special 
conditions, the 747-8/-8F 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.
    Special conditions, as defined in 14 CFR 11.19, are issued under 
Sec.  11.38, and become part of the type certification basis under 
Sec.  21.101.
    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 or similar 
novel or unusual design feature, or should any other model already 
included on the same type certificate be modified to incorporate the 
same or similar novel or unusual design feature, the special conditions 
would also apply to the other model under Sec.  21.101.

Novel or Unusual Design Features

    The Boeing Model 747-8/-8F airplane will incorporate the following 
novel or unusual design features: A four-post main landing gear system 
with two wing main landing gears and two body main landing gears.

Discussion

    The Boeing Model 747-8/-8F airplane will retain the landing gear 
arrangement which is unique to the 747 family of airplanes. The 
conventional arrangement for the main landing gear of transport 
category airplanes is two-underwing posts. The 747 was the first to 
introduce a four-post main landing gear arrangement, two underwing 
posts supplemented by two body posts. This arrangement was adopted to 
accommodate the then unprecedented increased weight and size of the 
Model 747 airplane.
    Existing regulations are written to address the conventional 
landing gear configuration commonly found on transport category 
airplanes. This being the case, they are not appropriate to address the 
unique features of the Boeing 747 design. The increased number of posts 
alters the load distribution between the gear units during landing and 
ground handling conditions addressed by the regulations. This 
arrangement also loads the airframe differently than conventional 
landing gear designs. The FAA determined that, while the general 
conditions addressed by Sec. Sec.  25.473 and 25.479 through 25.485 
were still applicable, specific details contained in these regulations 
may not be directly relatable to the four-post arrangement.
    In 1968 the FAA issued Special Condition A-4 to address the ground 
load requirements for the main landing gear system for Boeing Model 
747-100 series airplanes. That special condition provided clarification 
on the applicability of Sec. Sec.  25.473 and 25.479 through 25.485 to 
the Model 747 airplane. In 1971 Special Condition A-4 was amended to 
address Boeing Model 747 airplanes with the landing gear load evener 
system deleted or made inoperable.
    The FAA has determined that Special Condition A-4 is applicable to 
the 747-8/-8F series airplanes, provided that all the applicable part 
25 regulations cited in Special Condition A-4 (recorded as an enclosure 
to FAA Letter WE-120/8110 (CT3488WE-D) to the Boeing Company, dated May 
12, 1971) are upgraded to the latest amendment level (i.e., 25-117). 
Furthermore, as several of these regulations have been updated or 
consolidated, and acceptable methods of compliance have been described 
for some of these regulations via advisory circular (AC), new special 
conditions are needed to clarify the applicable requirements. By 
updating these special conditions, we are ensuring that the Boeing 
design provides an equivalent level of safety to conventional landing 
gear meeting these regulations.

Discussion of Comments

    Notice of proposed special conditions No. 25-09-05-SC for the 
Boeing Model 747-8/-8F airplanes was published in the Federal Register 
on April 27, 2009 (74 FR 19023). Airbus, an original equipment 
manufacturer, provided several specific comments.
    Airbus suggested that certain special conditions be revised to 
follow the intent of rule changes and guidance recommended by the 
Aviation Rulemaking Advisory Committee (ARAC). This committee, 
comprised of representatives from industry and the regulatory 
authorities, developed recommendations that would revise many of the 
ground load requirements in 14 CFR 25.
    While the FAA agrees with the ARAC recommendations, those 
recommendations have not yet been adopted into 14 CFR 25. Therefore, 
evaluation of the ARAC recommendations is not required per Sec.  
21.101, Designation of applicable regulations (the Changed Product 
Rule). Furthermore, the FAA does not believe that there is any safety 
concern that requires application of the ARAC recommendations. On past 
programs, the FAA has only applied parts of the ARAC recommendations, 
either by equivalent safety findings or by special conditions, and only 
when requested by an applicant. Even in those cases, the updated 
requirements have not been used in their entirety.
    As previously indicated, the proposed special condition was derived 
from the original 747 special condition and was updated to the latest 
amendment level. The service history of the 747 landing gear design 
indicates that the original special condition provides adequate design 
requirements. Furthermore, the landing gear design has not been 
significantly changed for the 747-8/-8F. Finally, the proposed special 
condition is an improvement on the original as it takes into account 
numerous updates to the rules and guidance material it references.
    Airbus proposed the following specific changes:
    1. The special conditions require consideration of the effects of 
runway crown for ground handling conditions, as defined in Sec.  
25.511(b)(4). Airbus suggested that these effects should also be 
considered for landing conditions as specified in the ARAC 
recommendations.
    FAA Response: While the ARAC recommendations represent an 
improvement in design standards, we do not believe consideration of 
runway crown is necessary. Furthermore, the FAA has not mandated this 
requirement on any other program.
    2. The special conditions include the following: ``The level 
landing criteria of Sec.  25.479 are directly applicable. The four main 
landing gear units must be assumed to contact the ground with the 
airplane longitudinal axis in a horizontal attitude.'' Airbus suggested 
that the second sentence is in conflict with the first, and that the 
conditions specified in the ARAC recommendations should be used.
    FAA Response: The second sentence is intended to clarify how Sec.  
25.479 is applied to the 747 design, which is not envisaged by the 
current requirement. The FAA has not mandated the level landing 
requirement from the ARAC recommendations on any other program.
    3. The special conditions include: ``The criteria of Sec.  25.495 
(ground turning loads) are directly applicable.'' Airbus suggests it is 
not correct to state that these criteria are directly applicable and 
that it would be more appropriate to apply the rational analysis 
described in the ARAC recommendations.
    FAA Response: We believe that application of this requirement can 
be directly applied, as has been done on previous 747 designs, and that 
such application is sufficiently conservative.

[[Page 51761]]

    4. With regard to the shock absorption test requirements of Sec.  
25.723, Airbus suggested that the test conditions be expanded as 
specified in the ARAC recommendations.
    FAA Response: We do not believe that using the latest ARAC 
recommendations is necessary, nor has this requirement been mandated on 
any other program to date.

Applicability

    As discussed above, these special conditions are applicable to the 
Boeing Model 747-8/-8F airplanes. Should Boeing 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 Boeing Model 747-8/-8F airplanes. 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.

The Special Conditions

0
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 Boeing Model 747-8/-8F airplanes.
    The requirements of Sec. Sec.  25.471, 25.473, and 25.479 through 
25.485 apply as follows:
    1. General. The general design criteria of Sec.  25.471 are 
directly applicable. The basic landing gear dimensional data must be 
expanded to include the additional main landing gear units.
    2. Ground Load Conditions and Assumptions. The criteria specified 
in Sec.  25.473 are applicable for the design landing conditions except 
as noted in paragraph 6 of these special conditions.
    3. Landing Gear Arrangement. The multiple oleo main landing gear 
configuration does not meet the ``conventional arrangement'' criterion 
of Sec.  25.477, with respect to the application of paragraphs 4 
through 7 of this special condition. Nevertheless, the landing impact 
design conditions must meet the intent of Sec. Sec.  25.473 through 
25.485.
    4. Level Landing Conditions. The level landing criteria of Sec.  
25.479 are directly applicable. The four main landing gear units must 
be assumed to contact the ground with the airplane longitudinal axis in 
a horizontal attitude.
    5. Tail-Down Landing Conditions. The airplane must be assumed to 
contact the ground in any tail down attitude between level and the 
maximum tail down attitude allowing clearance with the ground of each 
part of the airplane other than the main landing gear wheels. The 
airplane forward velocity component must be the most critical value 
from VL1 to 1.25 VL2 where VL1 and 
VL2 are defined in Sec.  25.481. Each main landing gear unit 
must be designed for its most critical combination of vertical load and 
drag load. All other criteria in Sec.  25.481, not superseded by the 
above criteria shall be directly applicable. The distribution of loads 
between the gear units for the effects of critical combinations of 
spin-up and spring-back loadings on the main landing gear units must be 
considered for the gear units and their supporting structure.
    6. One-Wheel Landing Conditions. Unless the airplane and landing 
gears are designed for equivalent or more critical conditions, the 
airplane will be assumed to land in a level pitch attitude at design 
landing weight with a descent velocity of 7 fps at the maximum roll 
angle attainable within the geometric limitations of the airplane with 
the contact velocities and gear landing conditions of Sec. Sec.  
25.479(a), (c) and (d).

    Note: This condition need not be coupled with either a 6 fps 
landing at maximum take off weight or a 12 fps reserve energy drop 
test.

    7. Side Load Conditions. On the main landing gear units, side loads 
of 80% of the vertical reaction (on one side) acting inward and 60% of 
the vertical reaction (on the other side) acting outward must be 
combined with one-half of the maximum vertical ground reactions 
obtained in the level landing, tail-down landing, or rolled attitude 
landing conditions. These loads shall be assumed applied at the ground 
contact point and to be resisted by the inertia of the airplane. Drag 
loads may be assumed to be zero.
    8. Rebound Landing Condition. The criteria of Sec.  25.487 are 
directly applicable.
    9. Ground Handling Conditions. The criteria of Sec.  25.489 are 
directly applicable. The effects of runway crown as defined in Sec.  
25.511(b)(4) shall be considered in distributing the loads to the 
individual main landing gear units. The ground reactions must be 
distributed to the individual landing gear units in a rational or 
conservative manner, accounting for airframe flexibility and shock 
strut and tire stiffness.
    10. Take-Off Run. The criteria of Sec.  25.491 are directly 
applicable. Compliance may be shown in accordance with Advisory 
Circular (AC) 25.491-1.
    11. Braked Roll Conditions. The criteria of Sec. Sec.  25.493(b), 
(c), and (d) shall be directly applicable. The formula in Sec.  
25.493(e) is not applicable to the B747 due to the 4-post gear 
arrangement.
    12. Turning. The criteria of Sec.  25.495 are directly applicable.
    13. Nose-Wheel Yaw. The criteria of Sec.  25.499 are directly 
applicable. The criteria are interpreted to apply braking to all main 
landing gear wheels on one side of the airplane centerline.
    14. Pivoting. The criteria of Sec.  25.503 are applied individually 
to each wing main landing gear unit. In addition, all main landing gear 
units must be designed for the scrubbing and/or torsion loads induced 
by pivoting about the most critical point consistent with the available 
main gear braking on one side of the airplane and the available thrust 
and torque on the airplane. Maximum static engine thrust must be 
considered only on the engines on the opposite side of the airplane 
centerline from the pivot point.
    15. Reversed Braking. The criteria of Sec.  25.507 are directly 
applicable, except that the phrase ``three point'' is expanded to 
include ``five point.''
    16. Towing Loads. The criteria of Sec.  25.509 are directly 
applicable.
    17. Fatigue Evaluation of Landing Gear. The criteria of Sec.  
25.573 at Amendment 25-0 are directly applicable to main landing gear 
units.
    18. Shock Absorption Tests. The criteria of Sec.  25.723 are 
directly applicable. Compliance may be shown in accordance with AC 
25.723-1.
    19. Substantiation of the design criteria must include a dynamic 
taxi and landing analysis.

    Issued in Renton, Washington, on September 29, 2009.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. E9-24339 Filed 10-7-09; 8:45 am]
BILLING CODE 4910-13-P