AD 99-07-06

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Boeing Model 767 series airplanes. This action requires repetitive inspections to detect cracking or damage of the forward and aft lugs of the diagonal brace of the nacelle strut, and follow-on actions, if necessary. This action also provides optional terminating action for the repetitive inspections. This amendment is prompted by a report that a fractured diagonal brace lug was found during a routine maintenance inspection. The actions specified in this AD are intended to detect and correct cracking of the diagonal brace of the nacelle strut, which could result in failure of the diagonal brace, and consequent fatigue failure of a strut secondary load path and separation of the engine and strut.

Final rule; request for comments

99-07-06 BOEING: Amendment 39-11091. Docket 99-NM-39-AD. \n\n\tApplicability: Model 767 series airplanes; as listed in Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998; 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 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 (f) 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 detect and correct cracking of the diagonal brace of the nacelle strut, which could result in failure of the diagonal brace, and consequent fatigue failure of a strut secondary load path and separation of the engine and strut, accomplish the following: \n\nInitial Inspection \n\n\t(a)\tPerform a detailed visual inspection to detect cracking or damage of the forward and aft lugs of the diagonal brace of the nacelle strut, on the left and right sides of the airplane, in accordance with Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998. Perform the inspection at the time specified in paragraph (a)(1) or (a)(2) of this AD, as applicable. \n\n\t\t(1)\tFor airplanes in Groups 1, 3, and 4: Inspect prior to the accumulation of 12,000 total flight cycles, or within 90 days after the effective date of this AD, whichever occurs later. \n\n\t\t(2)\tFor airplanes in Group 2: Inspect prior to the accumulation of 24,000 total flight cycles, or within 90 days after the effective date of this AD, whichever occurs later.\n\n Follow-On Actions\n \n\t(b)\tIf no cracking or damage is detected during the inspection required by paragraph (a) of this AD, repeat the inspection thereafter at the interval specified in paragraph (b)(1) or (b)(2) of this AD, as applicable, in accordance with Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998. Repeat the inspection until the actions specified by paragraph (d) or (e) of this AD have been accomplished. \n\n\t\t(1)\tFor airplanes in Groups 1, 3, and 4; and for airplanes in Group 2 on which the diagonal brace has accumulated more than 32,000 total flight cycles: Repeat the inspection at intervals not to exceed 1,000 flight cycles. \n\n\t\t(2)\tFor airplanes in Group 2 on which the diagonal brace has accumulated 32,000 or fewer total flight cycles: Repeat the inspection at intervals not to exceed 3,000 flight cycles. \n\n\t(c)\tIf any cracking or damage is detected during any inspection required by paragraph (a) or (b) of this AD, prior to further flight, remove the diagonal brace and perform additional inspections to detect damage of the strut secondary load paths, in accordance with Part 4 of Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998; and accomplish the requirements of paragraphs (c)(1) and, if applicable, (c)(2) of this AD. \n\n\t\t(1)\tPrior to further flight, replace the one-piece diagonal brace with a new three-piece diagonal brace, in accordance with Part 3 of the Accomplishment Instructions of the alert service bulletin. Such replacement constitutes terminating action for the requirements of this AD. \n\n\t\t(2)\tIf any additional damage of the alternate load paths is detected, prior to further flight, repair in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate; or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative who has been authorized by the Manager, Seattle ACO, to make such findings. \n\n\t(d)\tFor airplanes on which no cracking is detected during the inspection required by paragraph (a) of this AD, in lieu of accomplishing repetitive inspections in accordance with paragraph (b) of this AD, rework of the forward and aft lugs of the diagonal brace may be accomplished in accordance with Part 2 of the Accomplishment Instructions of Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998. If such rework is accomplished: Within 12,000 flight cycles after the rework, repeat the inspection required by paragraph (a) of this AD; and, prior to the accumulation of 37,500 total flight cycles on the diagonal brace, replace the one-piece diagonal brace with a new three-piece diagonal brace, in accordance with Part 3 of the Accomplishment Instructions of the alert service bulletin. Such replacement constitutes terminating action for the requirements of this AD. \n\nOptionalTerminating Action \n\n\t(e)\tReplacement of the one-piece diagonal brace with a new three-piece diagonal brace, in accordance with Part 3 of the Accomplishment Instructions of Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998, constitutes terminating action for the requirements of this AD. \n\nAlternative Methods of Compliance \n\n\t(f)\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 ACO. 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\nSpecial Flight Permits \n\n\t(g)\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\nIncorporation by Reference \n\n\t(h)\tExcept as specified by paragraph (c)(2) of this AD, the actions shall be done in accordance with Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998. 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 Effective Date \n\n\t(i)\tThis amendment becomes effective on April 12, 1999.

The FAA has received a report indicating that a fractured lug of the diagonal brace of the nacelle strut was found during a routine visual inspection of a Boeing Model 767 series airplane. The affected airplane had accumulated 36,247 flight hours and 17,677 flight cycles. \n\n\tSuch cracking has been attributed to migration of a bushing inside the lug bore. A migrated bushing could cause fretting damage to the lug bore, which could lead to the initiation of a crack. Subsequent propagation of that crack due to fatigue loading could result in complete fracture of the lug and consequent failure of the diagonal brace. Failure of the diagonal brace would place increased stress on the strut secondary load paths. Continued operation of the airplane with a failed diagonal brace could result in fatigue failure of a strut secondary load path. This condition, if not corrected, could result in separation of the engine and strut. \n\nExplanation of Relevant Service Information \n\n\tThe FAA has reviewed and approved Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998, which describes procedures for repetitive detailed visual inspections to detect cracking or damage of the forward and aft lugs of the diagonal brace of the nacelle strut, and follow-on actions, if necessary. Follow-on actions include, if cracking or damage is detected, replacement of the existing one-piece diagonal brace with a new three-piece diagonal brace, which eliminates the need for the repetitive inspections, and additional inspections of the strut secondary load paths to detect damage. For airplanes on which no cracking or damage is detected, the alert service bulletin describes procedures for optional rework of the diagonal brace, which allows repetitive inspections to be deferred, provided that the one-piece diagonal brace is replaced with a three-piece diagonal brace prior to the accumulation of 37,500 total flight cycles. \n\nExplanation of the Requirementsof the Rule \n\n\tSince an unsafe condition has been identified that is likely to exist or develop on other airplanes of the same type design, this AD is being issued to detect and correct cracking of the diagonal brace of the nacelle strut, which could result in failure of the diagonal brace, and consequent failure of a secondary load path and loss of the engine and strut. This AD requires repetitive detailed visual inspections to detect cracking or damage of the forward and aft lugs of the diagonal brace of the nacelle strut, and follow-on actions, if necessary. If no cracking or damage is detected, this AD provides for optional rework of the diagonal brace, which would allow the repetitive inspection threshold to be increased from 1,000 or 3,000 flight cycles, as applicable, to 12,000 flight cycles. If any cracking or damage is detected, this AD requires replacement of the existing one-piece diagonal brace with a new three-piece diagonal brace, which constitutes terminating actionfor the repetitive inspections; additional inspections of the strut secondary load paths to detect damage; and corrective actions, if necessary. This AD also provides for an optional replacement of the one-piece diagonal brace with a new three-piece diagonal brace, which constitutes terminating action for the repetitive inspection requirements of this AD. The actions are required to be accomplished in accordance with the alert service bulletin described previously, except as discussed below. \n\nDifferences Between Alert Service Bulletin and This AD \n\n\tOperators should note that the effectivity listing of the alert service bulletin is divided into four groups. However, Figure 1 of the alert service bulletin specifies procedures only for Groups 1, 2, and 3. The FAA has determined that airplanes in Group 4 are subject to the detailed visual inspection at the same threshold (12,000 total flight cycles), and the same corrective actions, if necessary, as airplanes in Groups 1 and 3.Operators also should note that, if the optional rework of the diagonal brace is accomplished, this AD requires re-inspection to detect cracking or damage of the diagonal brace lugs within 12,000 flight cycles. The alert service bulletin identifies the optional rework as "zero time rework"; however, the alert service bulletin does not clearly specify that the detailed visual inspection of the diagonal brace lugs should be repeated within 12,000 flight cycles after accomplishment of the rework. The FAA finds that, to ensure the safety of the fleet of affected airplanes, it is necessary to clarify the requirement to repeat the inspection of the diagonal brace within 12,000 flight cycles after rework. \n\n\tOperators also should note that, although the alert service bulletin specifies that the manufacturer may be contacted for disposition of certain repair conditions, this AD requires the repair of those conditions to be accomplished in accordance with a method approved by the FAA,or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative who has been authorized by the FAA to make such findings. \n\nInterim Action \n\n\tThis is considered to be interim action. The FAA currently is considering requiring the replacement of the existing one-piece diagonal brace with a new three-piece diagonal brace, which would constitute terminating action for the repetitive inspections required by this AD action. However, the planned compliance time for the installation of the three-piece diagonal brace is sufficiently long so that notice and opportunity for prior public comment will be practicable. \n\nDetermination of Rule's Effective Date \n\n\tSince a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days.\n\n Comments Invited \n\n\tAlthough this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified under the caption "ADDRESSES." All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed. \n\n\tComments are specifically invited on the overall regulatory, economic, environmental, and energy aspects ofthe rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket. \n\n\tCommenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 99-NM-39-AD." The postcard will be date stamped and returned to the commenter. \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 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\tThe FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, 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. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701. § 39.13 (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: