AD 99-27-05

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 767-200, -300, and -300F series airplanes was published in the Federal Register on August 4, 1998 (63 FR 41481). That action proposed to require replacement of the hydraulic reducer fitting in the return port of the alternate brake selector valve with a new restrictor fitting.

Comments Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.

Support for the Proposal One commenter concurs with the requirements of the proposed AD. The Air Transport Association (ATA) of America states that one of its members does not currently operate any airplanes affected by the proposed rule, and another member has no objection to the proposed rule.

Request to Revise the Discussion Section One commenter states that it does not agree that the brake vibration is caused by excessive flow of hydraulic fluid into the alternate system metering valves during gear retract braking, as described in the Discussion section of the proposed AD. The commenter contends that the gear retract braking system, common to Model 757, 747-400, and 777 series airplanes, and to Model 767 series airplanes equipped with steel brakes, has demonstrated trouble-free service experience in all of those airplane models without brake vibration. The brake vibration that has occurred during gear retract braking on Model 767 series airplanes equipped with Boeing part number (P/N) S160T300-series carbon brakes is attributed to the friction-material characteristics of the carbon brakes. Reducing the brake-pressure onset rate consistently reduces peak brake-torque amplitudes and brake vibration levels, when present. The new carbon brake, Boeing P/N S160T4000-210, for Model 767 series airplanes, uses a new carbon heatsink that has demonstrated extremely stable dynamic characteristics during laboratory and flight tests. Therefore, replacement of the existing carbon brakes, P/N S160T300-series, with the new carbon brake will, in itself, alleviate the high loads associated with brake vibration, without replacing the hydraulic restrictor fitting. The commenter recommends revising the Discussion section to read "Brake vibration during gear retract braking can be reduced on the existing carbon brakes by reducing the hydraulic flow to the brakes." The FAA does not concur that the cause of the brake vibration on Model 767-200, -300, and -300F series airplanes is due to the brake material and not the gear retract braking system. In addition, it is not necessary to revise the Discussion section, as that section does not appear in the final rule. Because the brake system comprises a group of components that include the brake friction material and gear retract brakes, which are subsets of the brake system, the FAA considers each component to be a contributor to the unsafe condition. Additionally, Boeing Service Bulletin 767-32-0152, dated June 6, 1996, and Revisions 1 and 2 of that service bulletin, do not specify that the cause of the vibration is the brake material, but only that the vibration occurs in airplanes equipped with carbon brakes. In fact, the third paragraph of the Summary section of Revision 1 of the service bulletin states that "Installation of the restrictor fitting will reduce the flow into the alternate-system metering valves during gear retract braking. This will reduce peak torque levels and vibration of the landing gear during retract braking." Request to Change the Applicability of the Proposal The commenter states that since the brake vibration is associated only with P/N S160T300-series carbon brakes, the applicability of the AD should be revised to read "Model 767-200, -300, and 300F series airplanes equipped with P/N S160T300 series carbon brakes; certified in any category." The FAA infers that the commenter considers that it is a combination of carbon brake material and the excessive onset of hydraulic pressure that results in the unsafe condition; and that brakes manufactured with a ceram-metallic composite, while benefiting from the change, do not exhibit the unsafe condition the FAA seeks to correct through the issuance of this AD. The FAA concurs that the brake vibration is associated only with airplanes equipped with Boeing P/N S160T300 series carbon brakes. The FAA also agrees with the manufacturer that including the specified part number in the applicability of the final rule correctly identifies those airplanes with the unsafe condition, and has revised the final rule accordingly. (The applicability of this AD continues to include the same airplanes "1 through 607 inclusive;" however, the term "line positions," which was used in the proposed AD, has been changed to "line numbers" in this AD.) Request to Revise Certain Terminology One commenter states that, with reference to an alternative means (method) of compliance (AMOC), an "equivalent" level of safety rather than an "acceptable" level of safety should be considered. The commenter provides no justification for its request. The FAA does not concur that the level of safety should be specified as "equivalent" rather than "acceptable." When considering any AMOC request, the Manager of the Seattle Aircraft Certification Office evaluates the request and determines whether the proposed AMOC request is acceptable (i.e., whether the proposed AMOC adequately addresses the unsafe condition). If so, the manager approves the request, even if it is not technically "equivalent" to the method of compliance required by the AD. No change to the final rule is necessary. Conclusion After 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 change previously described. The FAA has determined that this change will neither increase the economic burden on any operator nor increase the scope of the AD. Cost Impact There are approximately 373 Model 767-200, -300, and -300F series airplanes of the affected design in the worldwide fleet. The FAA estimates that 86 airplanes of U.S. registry will be affected by this AD, that it will take approximately 4 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 $104 per airplane. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $29,584, or $344 per airplane. The 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. Regulatory Impact The 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. For 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." List of Subjects in 14 CFR Part 39 Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. Adoption of the Amendment Accordingly, 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: PART 39 - AIRWORTHINESS DIRECTIVES 1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701. § 39.13 (Amended) 2. Section 39.13 is amended by adding the following new airworthiness directive: