AD 96-17-08

This amendment adopts a new airworthiness directive (AD), applicable to certain McDonnell Douglas Model DC-10-10, -15, -30, -40, and KC-10A (military) series airplanes, that requires modification of the AC generator control units. This amendment is prompted by reports of loss of electrical power from two generators and an engine that flamed out due to an overfrequency condition of a generator. The actions specified by this AD are intended to prevent an overfrequency condition of a generator, which could lead to the loss of all electrical power of the airplane.

Final rule.

96-17-08 MCDONNELL DOUGLAS: Amendment 39-9717. Docket 95-NM-177-AD. \n\n\tApplicability: Model DC-10-10, -15, -30, -40, and KC-10A (military) series airplanes, as listed in McDonnell Douglas Service Bulletin DC10-24-111 RO1, Revision 1, dated August 14 1995; 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 an overfrequency condition of the generator, which could result in loss of all electrical power of the airplane, accomplish the following: \n\n\t(a)\tWithin 2 years after the effective date of this AD, modify the AC generator control units (GCU) in accordance with McDonnell Douglas Service Bulletin DC10-24-111 RO1, Revision 1, dated August 14, 1995. \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 compliancewith 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 modification shall be done in accordance with McDonnell Douglas Service Bulletin DC10-24-111 RO1, Revision 1, dated August 14, 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(e)\tThis amendment becomes effective on September 23, 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-10-10, -15, -30, -40, and KC-10A (military) series airplanes was published in the Federal Register on January 3, 1996 (61 FR 134). That action proposed to require modification of the AC generator control units. \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\tThree commenters support the proposed rule. \n\nRequest Not to Adopt the Rule \n\n\tOne commenter requests that the proposed AD not be adopted as proposed. The commenter states that the modification (i.e., addition of a circuit that will provide overfrequency protection) proposed by the AD causes a significant reduction in the reliability of the generator control unit (GCU).The commenter notes that, following accomplishment of the proposed modification, it has experienced an increase of GCU removals and bus tie relay (BTR) lockouts on in-service airplanes. The commenter acknowledges that the subject modification may add a margin of operating safety to the electrical generator system of Model DC-10 series airplanes; however, the commenter notes that the margin may be eliminated with the reduction in the reliability of the GCU and increased BTR lockouts. Therefore, the commenter concludes that the FAA should investigate the root cause of the failure of the constant speed drive (CSD). \n\n\tThe FAA does not concur with the commenter's request that the proposal not be adopted. The FAA acknowledges that the subject modification may cause a reduction in the reliability of the GCU, which may lead to increased removals of the GCU; and may cause an increase in the BTR lockouts. However, the FAA has determined that the GCU's have a low failure rate, since the overfrequency protection circuit contains a minimum of parts; therefore, the reduction in the reliability of the GCU will be minimal. In addition, the FAA recognizes that the BTR lockouts may be a nuisance; however, the FAA finds that such lockouts will not adversely affect the safety of the fleet. Furthermore, the FAA has evaluated the root cause of the CSD failure and concluded that there are no assurances that could prevent the failure of the CSD. Therefore, the FAA finds that modification of the GCU's is necessary to provide overfrequency protection as a result of failure of the CSD. An overfrequency condition of a generator, if not corrected, could lead to the loss of all electrical power of the airplane. \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 419 Model DC-10-10, -15, -30, -40, and KC-10A (military) series of the affected design in the worldwide fleet. The FAA estimates that 276 airplanes of U.S. registry will be affected by this AD, that it will take approximately 5 work hours per airplane to accomplish the required actions, and that the average labor rate is $60 per work hour. Required parts will cost approximately $2,896 per generator control unit; there are 4 units per airplane. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $3,279,984, or $11,884 per airplane. \n\n\tThe 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\nRegulatory Impact \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 ofpower 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 part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows: \n\nPART 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: