AD 94-16-05 ACTIVE

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 767 series airplanes, that requires repetitive inspections to detect cracking, corrosion, and wear of various components of the main landing gear (MLG) brake assembly, and correction of discrepancies. This amendment is prompted by reports indicating that components in the MLG assembly have been damaged due to the consequences of vibration in the brake assembly. The actions specified by this AD are intended to minimize the exposure of the brake assembly to the consequences of a vibratory condition that could ultimately lead to failure of components of the MLG; such failure could severely affect the braking capability of the airplane while on the ground.

Final rule

94-16-05 BOEING: Amendment 39-8995. Docket 93-NM-218-AD. \n\n\tApplicability: Model 767 series airplanes equipped with carbon brakes, certificated in any category. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent the failure of components of the main landing gear, which could severely affect the braking capability of the airplane while on the ground, accomplish the following: \n\n\t(a)\tWithin 1,600 flight cycles after the effective date of this AD, and thereafter at intervals not to exceed 1,600 flight cycles, conduct inspections to detect cracking and corrosion of the pin that attaches the brake rod to the brake housing; to detect cracking of the brake torque arm bushings; and to detect wear of the brake rod bushings; in accordance with Part 1 of Boeing Service Bulletin 767-32-0128, Revision 1, dated March 31, 1994. If any discrepancy is detected in any part, replace or repair the part in accordance with the compliance schedule specified inFigure 1, Figure 2, or Figure 3 of the service bulletin, as applicable. \n\n\tNOTE 1: Inspections, replacement, and repairs performed prior to the effective date of this AD in accordance with Boeing Service Bulletin 767-32-0128, dated November 11, 1993, are considered to be in compliance with this paragraph. \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, Seattle 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, Seattle 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 Seattle 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 Boeing Service Bulletin 767-32-0128, Revision 1, dated March 31, 1994. 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 Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; 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 14, 1994.

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 Boeing Model 767 series airplanes was published in the Federal Register on March 15, 1994 (59 FR 11946). That action proposed to require inspections to detect cracking, corrosion, and wear of various components of the main landing gear (MLG) brake assembly, and correction of discrepancies. \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\nOne commenter supports the proposal. \n\n\tSeveral commenters request that the proposal be withdrawn. These commenters contend that AD 94-03-07, amendment 39-8814 (59 FR 7897, February 17, 1994), adequately addresses the safety concerns related to failures caused by the vibration phenomenon of the brakes. That AD is applicable to the same airplanes that would be affected by the proposal, and requires that operators incorporate modifications and perform several different types of inspections to detect cracking and other damage of various components of the MLG brake assembly. Additionally, one commenter advises that every operating airplane affected by AD 94-03-07 is currently in compliance with that AD and, due to the efforts of the operators of these airplanes, there has been a "dramatic effect" in addressing the known brake failure modes.\n \n\tThe FAA does not concur with the request to withdraw the AD. The issuance of AD 94-03- 07 was prompted by incidents of brake failure and by physical evidence, which indicated that certain components in the brake load path are subject to damage or failure due to the vibration phenomenon of the brakes. Such damage or failures can contribute to the overall failure of the braking system. While accomplishment of the requirements of AD 94-03-07 will minimize the likelihood or effect of failures of certain components within the brake system, accomplishment of the repetitive inspection requirements of this new AD will address potential damage that could further aggravate the identified vibration phenomenon. While there have been no in-service incidents of failure of certain of these specific components, the FAA has determined that the potential exists for such failures to occur, due to the configuration of the MLG brake assembly and the continuing occurrences of the vibration phenomenon of the brakes. If the failure of the subject components were to occur, it could further aggravate the vibratory condition and weaken the brake load path, possibly leading to further failures or loss of braking. No evidence has been submitted to the FAA to indicate that this potential for failure does not exist, or to justify that inspection of these components is not necessary. In light of these factors, the FAA has determined that this final rule is both appropriate and warranted.\n \n\tOne commenter states that the proposed inspections to detect corrosion and damage to the brake hardware are currently part of operators' maintenance programs. Prudent operators would be expected to adjust their maintenance programs to reflect the changes in the inspections and inspection intervals recommended by Boeing Service Bulletin 767-32-0128 (which is referenced in the proposal). The commenter contends that the incidents upon which the proposed AD and AD 94-03-07 are based are the result of design defects rather than improper maintenance; therefore, an operator's maintenance program should not have to be revised via an AD in order to address the safety concern. The commenter suggests that the FAA should not require the operator's maintenance program to be revised unless it can show that the maintenance program is inadequate. In this regard, the commenter requests that the FAA review its justification for the proposed rule to ensure that it is sufficient to satisfy the requirements of part 39 of the Federal Aviation Regulations (FAR) (14 CFR part 39), "Airworthiness Directives." \n\n\tThe FAA concurs with the commenter's observation that the unsafe condition addressed by this AD action is the result of a design deficiency and not a maintenance deficiency; however, the FAA does not concur with the commenter's inference that this AD is not justified. This commenter appears to be confusing the basis for finding of an unsafe condition with the appropriate means of addressing the unsafe condition. While it is true that the unsafe condition is based on a design deficiency of the MLG assembly, there currently is no permanent "design fix" to eliminate the problem. Therefore, although a design fix would be the ultimate intention, the FAA has determined that the accomplishment of the inspection requirements of this AD, in the interim, is necessary in order to minimize the occurrence of brake failures due to the brake vibration phenomenon and to ensure that an acceptable level of safety is maintained. With regard to the commenter's statement concerning maintenance programs, even though a parallel inspection action currently may be part of an operator's maintenance program, this AD serves as the means available to the FAA for mandating the appropriate inspection actions and ensuring their accomplishment at timely intervals by all affected operators. \n\n\tFurther, according to part 39 of the FAR, the issuance of an AD must be based on the finding that an unsafe condition exists or is likely to develop in aircraft of a particular type design. This AD is prompted by what the FAA has determined to be an unsafe condition to which Model 767 series airplanes equipped with carbon brakes are subject. That unsafe condition entails the failure of MLG components and the subsequent loss of braking capability, which is brought about by the effects of a vibration phenomenon that is known to exist in the brake assembly of these airplanes. The FAA also has determined that repetitive inspections of the affected area must be mandated in order to minimize the failure of the components and to ensure that safety is not degraded. The appropriate vehicle for mandating such action to correct an unsafe condition is the airworthiness directive. Accordingly, the issuance of this AD is justified under part 39 of the FAR. \n\n\tOne commenter requests an explanation of why the requirements of AD 94-03-07 are considered interim action. The FAA responds by noting that it considers the requirements of both AD 94-03-07 as well as this new AD to be interim action. The accomplishment of the requirements of these AD's is intended to minimize the occurrence of brake failures due to the brake vibration phenomenon. These actions do not eliminate the vibration phenomenon itself, however, as has been verified by a recent incident that occurred in March 1994. During that incident, an airplane that was in compliance with AD 94-03-07 experienced a rejected takeoff inwhich there was no detected brake loss, but brake components were found to be fractured or damaged during an inspection performed after the incident occurred. The damage that was sustained as a result of that incident was primarily in components other than those addressed by AD 94-03-07. It is apparent that failure of the brake components due to vibration can still occur. The FAA maintains that design changes are needed that will eliminate or significantly reduce the vibration phenomenon recognized in the Model 767 carbon brake system, or significantly reduce the occurrence of failures in the brake load path. The FAA considers that the actions required by AD 94-03-07 and by this new AD are interim actions until such design changes are developed and available. \n\n\tSeveral commenters request that the proposed compliance terms be revised from "hours time-in-service" to "flight cycles." These commenters point out that the procedures specified in the referenced Boeing service bulletinare in terms of flight cycles, not hours. The FAA concurs. The reference to "hours time-in-service" that appeared in the proposal was an error. The wording of the final rule has been corrected to specify "flight cycles". This correction will not impose any additional burden on affected operators; it will relieve operators from having to perform the inspections earlier or more often than is actually necessary. \n\n\tThese same commenters request that the compliance time for the inspections that would be required by paragraph (a) be revised from the proposed 1,500 hours time-in-service to 1,600 flight cycles. The commenters state that AD 94-03-07 requires that the rod linkage be inspected at intervals of 800 flight cycles; therefore, the adoption of a 1,600-flight cycle interval for the proposed inspections would allow some of them to be accomplished concurrently with those of AD 94-03-07. This will simplify scheduling and eliminate duplication of work for affected operators. The FAAconcurs. In addition to considering the reasons presented by these commenters, the FAA has reviewed and approved Revision 1 of Boeing Service Bulletin 767-32-0128, dated March 31, 1994. Among other things, this revised version of the service bulletin recommends that inspections of the pins, the brake torque arm bushings, and the brake rod bushings begin within 1,600 flight cycles and be repeated at intervals of 1,600 flight cycles. Paragraph (a) of the final rule has been revised to specify a 1,600-flight cycle inspection interval, and to reference the revised version of the service bulletin as the appropriate source of service information. \n\n\tAnother commenter requests that the inspections of the bulkhead, keeper pin, and brake attach pin, as proposed by paragraph (b), be eliminated. This commenter points out that modification of the brake rod pin assembly and the brake attach pin retainer, which is required by AD 94-03-07, has significantly strengthened the brake load path inthis area. There has been no indication that this area continues to be a problem area once the modification is installed. The FAA concurs with the commenter's request to delete the proposed inspections. The requirements of AD 94-03-07 eliminated the cross bolts at the brake rod attach pin, thereby eliminating one of the failure modes in the brake load path that had accounted for a significant number of brake loss incidents. The modification required by AD 94-03-07 improves the brake load path in the brake- to-brake rod attachment area. In light of this, the FAA has determined that the inspections proposed in paragraph (b) of the notice are not necessary, and has deleted them from the final rule. The FAA notes that Part 2 of Revision 1 of Boeing Service Bulletin 767-32-0128 provides instructions for inspecting the modified area for corrosion or damage. Although those inspections may be "value added," the FAA does not consider them necessary to improve the safety of the brake system. \n\n\tOne commenter provides an update on the number of airplanes affected by the proposed AD. The information provided by this commenter indicates that the worldwide number has risen from 289 airplanes (at the time the proposal was issued) to 308 airplanes; and the U.S.-registered number has risen from 71 airplanes to 77 airplanes. The FAA has revised the economic impact information, below, accordingly. \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 308 Model 767 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 77 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. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $42,350, or $550 per airplane, per inspection cycle. \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 certifythat 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\n PART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1.\tThe authority citationfor part 39 continues to read as follows: Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89. § 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 Boeing\nCommercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. 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 Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Kristin Larson, Aerospace Engineer, Systems &\nEquipment Branch, ANM-130S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (206) 227-1760; fax (206) 227-1181.