AD 96-01-09

This amendment adopts a new airworthiness directive (AD), applicable to certain McDonnell Douglas Model DC-9-80 series airplanes and Model MD-88 airplanes, that requires installation of hydraulic line restrictors in the main landing gear (MLG), and modification of the hydraulic damper assembly of the MLG. This amendment is prompted by reports of vibration occurring in the MLG during landing; in some cases, such vibration has led to the collapse of the MLG. The actions specified by this AD are intended to prevent incidents of vibration in the MLG, which can adversely affect the integrity of the MLG.

Final rule.

96-01-09 McDONNELL DOUGLAS: Amendment 39-9485. Docket 95-NM-91-AD.\n\n\tApplicability: Model DC-9-81 (MD-81), -82 (MD-82), -83 (MD-83), and -87 (MD-87) series airplanes, and Model MD-88 airplanes; certificated in any category; and listed in the following McDonnell Douglas Service Bulletins:\n\n\tMcDonnell Douglas MD-80 Service Bulletin MD80-32-276, \n\t\tdated March 31, 1995; and \n\n\tMcDonnell Douglas MD-80 Service Bulletin MD80-32-278, \n\t\tdated March 31, 1995.\n\n\tNOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must use the authority provided in paragraph (c) of this AD to request approval from the FAA. This approval may address either no action, if the current configuration eliminates the unsafe condition; or different actions necessary to address the unsafe condition described in this AD. Such a request should include an assessment of the effect of the changed configuration on the unsafe condition addressed by this AD. In no case does the presence of any modification, alteration, or repair remove any airplane from the applicability of this AD.\n\n\tCompliance: Required as indicated, unless accomplished previously.\n\n\tTo reduce the possibility of vibration in the main landing gear (MLG) that can adversely affect its integrity, accomplish the following:\n\n\t(a)\tFor airplanes listed in McDonnell Douglas MD-80 Service Bulletin MD80-32-276, dated March 31, 1995, that have not been previously modified (installation of brake line restrictors) in accordance with McDonnell Douglas MD-80 Service Bulletin 32-246: Within 9 months after the effective date of this AD, install filtered brake line restrictors in the MLG hydraulic brake system in accordance with McDonnell Douglas MD-80 Service Bulletin MD80-32-276, dated March 31, 1995, or Revision 1, dated October 17, 1995.\n\n\tNOTE 2: Installation of the filtered restrictors in accordance with the instructions contained in McDonnell Douglas MD-80 Alert Service Bulletin MD80-A32-286, dated September 11, 1995, is considered acceptable for compliance with paragraph (a) of this AD.\n\n\t(b)\tFor airplanes listed in McDonnell Douglas MD-80 Service Bulletin MD80-32-278, dated March 31, 1995: Within 36 months after the effective date of this AD, modify the hydraulic damper assembly (by removing shims, increasing bolt torque, and incorporating changes to increase the volume of fluid passing between the two damper chambers) in accordance with McDonnell Douglas MD-80 Service Bulletin MD80-32-278, dated March 31, 1995, or Revision 1, dated September 6, 1995.\n\n\t(c)\tAn alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approvedby the Manager, Los Angeles Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Los Angeles ACO.\n\n\tNOTE 3: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Los Angeles ACO.\n\n\t(d)\tSpecial flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.\n\n\t(e)\tThe installation shall be done in accordance with McDonnell Douglas MD-80 Service Bulletin MD80-32-276, dated March 31, 1995; or McDonnell Douglas MD-80 Service Bulletin MD80-32-276, Revision 1, dated October 17, 1995. The modification shall be done in accordance with McDonnell Douglas MD-80 Service Bulletin MD80-32-278, dated March 31, 1995; or McDonnell Douglas MD-80 Service Bulletin MD80-32-278, Revision 1, dated September 6, 1995. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from McDonnell Douglas Corporation, 3855 Lakewood Boulevard, Long Beach, California 90846, Attention: Technical Publications Business Administration, Department C1-L51 (2-60). Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA, Los Angeles Aircraft Certification Office, Transport Airplane Directorate, 3960 Paramount Boulevard, Lakewood, California; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.\n\n\t(f)\tThis amendment becomes effective on February 26, 1996.

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to certain McDonnell Douglas Model DC-9-80 series airplanes and Model MD-88 airplanes was published in the Federal Register on September 26, 1995 (60 FR 49523). That action proposed to require installation of hydraulic line restrictors in the main landing gear (MLG), and modification of the hydraulic damper assembly of the MLG.\n\n\tInterested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.\n\n\tFour commenters support the proposal.\n\n\tOne commenter requests that the FAA revise the proposal to include references to later revisions of the pertinent service bulletins, which were recently released. The FAA concurs. Subsequent to the issuance of the proposal, the FAA reviewed and approved Revision 1 of McDonnell DouglasMD-80 Service Bulletin MD80-32-276, dated October 17, 1995; and Revision 1 of McDonnell Douglas MD-80 Service Bulletin MD80-32-278, dated September 6, 1995. These revisions are essentially identical to the original issues of the service bulletins (which were referenced in the proposal), but contain additional clarifying information. Additionally, the FAA has reviewed and approved McDonnell Douglas MD-80 Alert Service Bulletin MD80-A32-286, dated September 11, 1995, which contains, among other things, instructions for installing filtered restrictors in the MLG hydraulic brake system. The FAA has revised the final rule to include these newly released service bulletins as additional sources of appropriate service instructions.\n\n\tOne commenter requests that paragraph (a) of the proposal be revised to extend the compliance time for installation of the brake line restrictors. This commenter is concerned that an ample number of required parts will not be available to modify its large fleet within the proposed compliance time of 9 months. The FAA does not concur that an extension of the compliance time is necessary. In McDonnell Douglas MD-80 Service Bulletin MD80-32-276, the manufacturer recommended that the installation of the restrictors be accomplished on the affected fleet within 12 months. Since the latest revision of that service bulletin was issued on October 17, 1995, the FAA considers it to be substantiation that the manufacturer can support parts production and delivery for the affected fleet through October 17, 1996. Since compliance with this AD is required by approximately that same date, the FAA does not foresee that the availability of required parts will be a problem for operators. However, under the provisions of paragraph (c) of the final rule, the FAA may approve requests for adjustments to the compliance time if data are submitted to substantiate that such an adjustment would provide an acceptable level of safety.\n\n\tOne commenter requeststhat the FAA defer action on the proposed requirements of paragraph (b), which would require operators to modify the hydraulic damper assembly. This commenter contends that further research and testing of the structural integrity of the reservoir should be accomplished first to substantiate that the installation of the hydraulic brake line restrictors (that would be required by paragraph (a) of the proposal) will successfully curb the vibration problems. This commenter claims that, if the most vulnerable part of the damper design is the reservoir, then no amount of "efficiency improvements" to the basic damper assembly will help. The FAA does not concur with the commenter's request. The FAA finds that the previous evaluations of this problem confirm that the reservoir failures are the result of the landing gear vibration, and are not a preceding failure that contributes to the vibration. Based on these evaluations and other data obtained to date, the FAA maintains that the modification required by paragraph (b) is both warranted and appropriate.\n\n\tAfter careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule with the changes previously described. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.\n\n\tThere are approximately 1,100 Model DC-9-80 series airplanes and Model MD-88 airplanes of the affected design in the worldwide fleet. The FAA estimates that 600 airplanes of U.S. registry will be affected by this proposed AD.\n\n\tAccomplishment of the installation of the brake line restrictor, as described in McDonnell Douglas MD-80 Service Bulletin MD80-32-276, will take approximately 4 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Required parts will cost approximately $928 per airplane. Based on these figures, the cost impact of this installation on U.S. operators is estimated to be $700,800, or $1,168 per airplane.\n\n\tAccomplishment of the modification of the hydraulic damper assembly, as described in McDonnell Douglas MD-80 Service Bulletin MD80-32-278, will take approximately 6 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Required parts will cost approximately $4,000 per airplane. Based on these figures, the cost impact of this modification on U.S. operators is estimated to be $2,616,000, or $4,360 per airplane.\n\n\tBased on the figures discussed above, the FAA estimates that the cost impact of this AD on U.S. operators would be approximately $3,316,800, or $5,528 per airplane. This cost impact figure is based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted.\n\n\tThe regulations adopted herein will not have substantialdirect effects 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, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.\n\n\tFor the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) 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 final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES."\n\nList of Subjects in 14 CFR Part 39\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.\n\nAdoption of the Amendment\n\tAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:\n\nPART 39 - AIRWORTHINESS DIRECTIVES\n\t1. The authority citation for part 39 continues to read as follows:\nAuthority: 49 USC 106(g), 40101, 40113, 44701. \n\n§ 39.13 - (Amended)\n\t2. Section 39.13 is amended by adding the following new airworthiness directive: