AD 94-08-03 ACTIVE

This amendment adopts a new airworthiness directive (AD), applicable to certain McDonnell Douglas Model MD-11 series airplanes, that requires visual inspection to detect inward buckling of the left and right main landing gear (MLG) pistons, and modification or replacement of the rebound check valves with new valves. If inward buckling is detected, this AD also requires replacement of the MLG piston with a serviceable piston. This amendment is prompted by failures of the MLG piston on Model DC-10 series airplanes. The actions specified by this AD are intended to prevent failure of the MLG piston and the subsequent reduced controllability of the airplane during landing.

Final rule.

94-08-03 MCDONNELL DOUGLAS: Amendment 39-8874. Docket 93-NM-20-AD. \n\n\tApplicability: Model MD-11 series airplanes, as listed in McDonnell Douglas MD-11 Service Bulletin 32-19, Revision 1, dated August 12, 1993, certificated in any category. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent failure of the main landing gear (MLG) piston and the subsequent reduced controllability of the airplane during landing, accomplish the following: \n\n\t(a)\tWithin 2 years after the effective date of this AD, perform a visual inspection to detect inward buckling of the left and right MLG pistons, in accordance with McDonnell Douglas MD-11 Service Bulletin 32-19, Revision 1, dated August 12, 1993. \n\n\t\t(1)\tIf any piston is found to be buckled inwardly, prior to further flight, accomplish the requirements of paragraphs (a)(1)(i) and (a)(1)(ii) of this AD, in accordance with McDonnell Douglas MD-11 Service Bulletin 32-19, Revision 1, dated August 12, 1993:(i)\tReplace that MLG piston with a serviceable piston; and \n\n\t\t\t(ii)\tModify or replace the rebound check valves with new valves. \n\n\t\t(2)\tIf no piston is found to be buckled inwardly, prior to further flight, modify or replace the rebound check valves with new valves in accordance with McDonnell Douglas MD-11 Service Bulletin 32-19, Revision 1, dated August 12, 1993. \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: 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 Federal Aviation Regulations (FAR) 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 inspection, replacement, and modification shall be done in accordance with McDonnell Douglas MD-11 Service Bulletin 32-19, Revision 1, dated August 12, 1993. 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, P.O. Box 1771, Long Beach, California 90801-1771, Attention: Business Unit Manager, Technical Administrative Support, Department L51, M.C. 2-98. 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 ACO, 3229 East Spring Street, Long Beach, 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 May 23, 1994.

A proposal to amend part 39 of the Federal Aviation Regulations to include an airworthiness directive (AD) that is applicable to certain McDonnell Douglas Model MD-11 series airplanes was published in the Federal Register on September 29, 1993 (58 FR 50871). That action proposed to require visual inspection to detect inward buckling of the left and right main landing gear (MLG) pistons, and modification or replacement of the rebound check valves with new valves. If inward buckling is detected, that action also proposed to require replacement of the MLG piston with a serviceable piston. \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\tOne commenter supports the proposed rule. \n\n\tOne commenter, the Air Transport Association (ATA) of America, on behalf of one of its member operators, objects to the proposed requirement to modify or replace rebound check valves on the MLG pistons with new valves. This commenter suggests that the requirement is unnecessary, due to the fact that the piston assemblies installed on the Model MD-11 series airplanes are substantially stronger than those installed on the Model DC-10 series airplanes. The FAA does not concur that this rule is unnecessary. Although the pistons installed on Model MD-11 series airplanes are generally stronger than those installed on Model DC-10 series airplanes, the FAA has reviewed an analysis conducted by the manufacturer, which supports the FAA's finding that the thicker piston walls (a few thousandths of an inch) on pistons installed on Model MD-11 series airplanes will not adequately prevent inward buckling of MLG pistons. Model MD-11 series airplanes have a higher maximum landing weight than Model DC-10 series airplanes. Under certain conditions, these higher landing weights result in higher pressure loads in the rebound chamber. Therefore, the FAA hasdetermined that the installation of new or modified rebound check valves will prevent failure of MLG pistons and the subsequent reduced controllability of the airplane during landing. \n\n\tSeveral commenters request extensions of the proposed two-year compliance time. One of these commenters requests that the proposed compliance time be extended to eight years, which would allow operators to accomplish the proposed modification or replacement of the rebound check valves coincidentally with the operator's regularly scheduled maintenance ("D" check) at which time the MLG would be scheduled to be changed. Another commenter requests that the compliance time coincide with AD 92-27-18, Amendment 39-8453 (58 FR 5259, January 21, 1993), which is applicable to certain DC-10 series airplanes, to require visual inspection to detect inward buckling of the left and right MLG pistons, and modification or replacement of the rebound check valves with new valves. \n\n\tThe FAA does not concur with these commenters' request to extend the compliance time. The FAA has determined that the compliance time, as proposed, represents the maximum interval of time allowable for the affected airplanes to continue to operate prior to accomplishing the required modification or replacement of the rebound check valves without compromising safety. Additionally, the FAA finds that the integrity of the MLG cannot be ensured for a period of eight years without modifying or replacing the rebound check valves. Further, in light of the reported incident during which the MLG piston on a Model DC-10-10 series airplane failed, and the safety implications of a failed MLG piston and the subsequent reduced controllability of the airplane during landing, the FAA finds that an extension of the compliance time would adversely affect safety of the affected airplanes. Although the MLG's installed on Model DC-10 series airplanes and Model MD-11 series airplanes are similar in basic design, the ultimate strength capability of the MLG's differ significantly. In developing the compliance time of 24 months, the FAA based its finding upon, among other factors, the potential of the affected airplanes to be exposed to conditions that may result in buckling of the MLG pistons. The FAA finds that the higher landing maximum weights of the Model MD-11 series airplanes may result in higher pressure loads in the rebound chamber, which may result in a greater rate of failure on these MLG's. Therefore, the FAA finds the 24-month compliance time justifiable and appropriate to address this unsafe condition. \n\n\tSeveral commenters note that the economic impact information in the proposal was inaccurate. One of these commenters states that the FAA's estimate of 9.5 work hours per airplane to accomplish the proposed actions is extremely low. One operator estimates that its cost to implement the actions proposed by this AD will be approximately $65,000. One commenter states that a more accurate estimation would be 30 work hours, as is specified in McDonnell Douglas MD-11 Service Bulletin 32-19, Revision 1, dated August 12, 1993 (referenced in the proposal as the appropriate source of service information). The FAA concurs, in part, with these commenters observations. The approximate number of work hours required to accomplish the required actions, which was presented in the economic impact information of the notice, was provided to the FAA by the manufacturer, and was based on the best data available at that time. The FAA now recognizes that the number used in the proposal did not include the .5 work hour required to inspect the MLG pistons, although it did include the time required to modify and install the rebound check valves. In light of this, the number of work hours in the economic impact information, below, has been increased to 10 work hours. The cost analysis in AD rulemaking actions typically does not include planning time, aircraft preparation time, time to gain access andremove parts, or time to raise and lower the aircraft; accordingly, the cost estimate, below, does not include this data. \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 63 Model MD-11 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 22 airplanes of U.S. registry will be affected by this AD, that it will take approximately 10 work hours per airplane to accomplish the required actions, and that the average labor rate is $55 per work hour. Required parts will cost approximately $1,251 per airplane. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $39,622, or $1,801 per airplane. \n\n\tThe total cost impact figure discussed above 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 substantial direct 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\n\tAir 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 14 CFR part 39 of the Federal Aviation Regulations as follows: \n\nPART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1.\tThe authority citation for part 39 continues to read as follows: \n\nAuthority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89. \n\n§ 39.13 - (Amended) \n\n\t2.\tSection 39.13 is amended by adding the following new airworthiness directive:

The service information referenced in this AD may be obtained from McDonnell Douglas Corporation, P.O. Box 1771, Long Beach, California 90801-1771, Attention: Business Unit Manager, Technical Administrative Support, Department L51, M.C. 2-98. This information may be examined at the Federal Aviation Administration (FAA), Transport Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA, Transport Airplane\nDirectorate, Los Angeles Aircraft Certification Office, 3229 East Spring Street, Long Beach, California; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Maureen Moreland, Aerospace Engineer, Airframe Branch, ANM-121L, FAA, Transport Airplane Directorate, Los Angeles Aircraft Certification Office, 3229 East Spring Street, Long Beach, California 90806-2425; telephone (310) 988-5238; fax (310) 988-5210.