Source: https://www.federalregister.gov/documents/2009/10/08/E9-24339/special-conditions-boeing-model-747-8-8f-airplanes-structural-design-requirements-for-four-post-main
Timestamp: 2017-10-21 17:58:50
Document Index: 235491469

Matched Legal Cases: ['art 25', '§\u200921', '§\u200911', '§\u200921', 'art 25', '§\u200921', '§\u200925', '§\u200925', '§\u200925', '§\u200925', '§\u200925', '§\u200925', '§\u200925', '§\u200925']

A Rule by the Federal Aviation Administration on 10/08/2009
Docket No. NM403
Special Conditions No. 25-385-SC
https://www.federalregister.gov/d/E9-24339 https://www.federalregister.gov/d/E9-24339
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.
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.
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 Start Printed Page 51760unusual design feature, special conditions are prescribed under the provisions of § 21.16.
Special conditions, as defined in 14 CFR 11.19, are issued under § 11.38, and become part of the type certification basis under § 21.101.
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.
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.
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 § 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 § 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 § 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 § 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 § 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.Start Printed Page 51761
4. With regard to the shock absorption test requirements of § 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.
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 § 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 § 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.
10. Take-Off Run. The criteria of § 25.491 are directly applicable. Compliance may be shown in accordance with Advisory Circular (AC) 25.491-1.
Issued in Renton, Washington, on September 29, 2009.
[FR Doc. E9-24339 Filed 10-7-09; 8:45 am]