AD 96-21-01

This amendment adopts a new airworthiness directive (AD), applicable to certain McDonnell Douglas Model DC-9 series airplanes, that requires either replacement or modification of the hydraulic damper assembly. This amendment is prompted by reports indicating that insufficient damping of the hydraulic shimmy damper in the main landing gear (MLG) can allow high torsional vibration to occur. The actions specified by this AD are intended to prevent such vibration, which can damage the MLG assembly and lead to its collapse.

Final rule.

96-21-01 McDONNELL DOUGLAS: Amendment 39-9777. Docket 96-NM-91-AD. \n\n\tApplicability: Model DC-9-10, -20, -30, -40, and -50 series airplanes, and C-9 (military) airplanes; as listed in McDonnell Douglas Service Bulletin DC9-32-289, dated March 7, 1996; certificated in any category. \n\n\tNOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been otherwise 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 request approval for an alternative method of compliance in accordance with paragraph (b) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent high torsional vibration from occurring, which can damage the main landing gear (MLG) assembly and lead to its collapse, accomplish the following: \n\n\t(a)\tWithin 24 months after the effective date of this AD, either replace or modify the MLG hydraulic damper assembly, in accordance with the procedures specified as either "Option 1" or "Option 2," respectively, in McDonnell Douglas Service Bulletin DC9-32-289, dated March 7, 1996. \n\n\t(b)\tAn alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by 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 2: 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(c)\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(d)\tThe actions shall be done in accordance with McDonnell Douglas Service Bulletin DC9-32-289, dated March 7, 1996. 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, Transport Airplane Directorate, Los Angeles Aircraft Certification Office, 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(e)\tThis amendment becomes effective on November 14, 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 series airplanes and C-9 (military) airplanes was published in the Federal Register on July 10, 1996 (61 FR 36307). That action proposed to require either replacing or modifying the hydraulic damper assembly. \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\nSupport for the Proposal \n\n\tFour commenters support the proposal. \n\nRequest to Withdraw Proposal \n\n\tOne commenter contends that all reports of torsional vibration that resulted in torque link separations and/or breakage of the apex bolt occurred on Model DC-9-80 series airplanes. Given the number of Model DC-9 series airplanes in service and the number of landings logged on them without reports of torsional vibration caused by insufficient damping, the commenter considers the AD to be unwarranted. Further, this commenter states that the modification should not be mandated; operators should be allowed to accomplish it at their own discretion during a regularly scheduled maintenance visit. \n\n\tFrom these comments submitted, the FAA infers that the commenter requests that the proposed rule be withdrawn; in which case, the FAA does not concur. The commenter is incorrect in stating that the problems associated with torsional vibration have occurred only on Model DC-9-80 series airplanes. Such incidents and consequent damage have occurred on several Model DC-9 series airplanes as well. As detailed in the preamble to the notice, the MLG torque link broke on one airplane and, on another airplane, the nut was stripped off of the torque link apex bolt; both of these discrepancies were the result of insufficient damping of the MLG hydraulic shimmy damper. This fact alone affirms the need for this AD action. \n\n\tAs for mandating the modification, the FAA points out that this AD provides operators with the option of either modifying the damper assembly or replacing it with an improved assembly. The compliance time of 24 months assures that operators will be able to schedule the accomplishment of either of these actions during a normal maintenance interval. \n\nConclusion \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 as proposed. \n\nCost Impact \n\n\tThere are approximately 878 Model DC-9 series airplanes and C-9 (military) airplanes of the affected design in the worldwide fleet. The FAA estimates that 590 airplanes of U.S. registry will be affected by this AD. \n\n\tTo accomplish the replacement will take approximately 5.9 work hours per airplane, at an average labor rate of $60 per work hour. Required parts will cost approximately$11,139 per airplane (two assemblies at $5,569 each). Based on these figures, the cost impact of the replacement action on U.S. operators is estimated to be $11,492 per airplane. \n\n\tTo accomplish the required modification will take approximately 10.9 work hours per airplane, at an average labor rate of $60 per work hour. Required parts will cost approximately $2,907 per airplane. Based on these figures, the cost impact of the modification action on U.S. operators is estimated to be $3,561 per airplane. \n\n\tBased on the figures discussed above, the cost impact of this AD on the U.S. fleet is between $2,100,990 and $6,780,280. These cost impact figures are 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\nRegulatory Impact \n\n\tThe regulations adopted herein will not have substantial direct effects on the States, on the relationshipbetween 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 39Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\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\n PART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1. The authority citation for part 39 continues to read as follows: \n\nAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\n§ 39.13 - (Amended) \n\n\t2. Section 39.13 is amended by adding the following new airworthiness directive: