AD 94-14-04

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Boeing Model 757 series airplanes. This action requires inspection to detect cracking of the lower spar chord of the engine strut, removal of the stiffener straps from the mid-chord, inspection of the fastener holes, and modification or repair. This amendment is prompted by a report of cracking in the lower spar chord of an engine strut. The actions specified in this AD are intended to prevent cracking in the lower spar chord of the engine strut, which could result in the inability of the strut to carry required engine support loads.

Final rule; request for comments.

94-14-04 BOEING: Amendment 39-8956. Docket 94-NM-85-AD. \n\n\tApplicability: Model 757 series airplanes having airplane line numbers 2, 4, 5, 9 through 13 inclusive, 21, 26, 114, and 115, certificated in any category. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent cracking in the lower spar chord of the engine strut, which could result in the inability of the strut to carry required engine support loads, accomplish the following: \n\n\t(a)\tWithin 60 days after the effective date of this AD, perform an eddy current inspection to detect cracking of the lower chord, in accordance with Boeing Service Bulletin 757-54-0028, dated March 31, 1994. \n\n\t(b)\tIf no cracking is detected during the inspection required by paragraph (a) of this AD, prior to the accumulation of 1,500 landings after accomplishment of the inspection, remove the stiffener straps from the mid-chord of the inboard and outboard sides of the strut, and perform an open hole eddy current inspection to detect cracking of the fastener holes in the mid-chord, in accordance with Boeing Service Bulletin 757-54-0028, dated March 31, 1994. \n\n\t\t(1)\tIf no cracking is detected in the mid-chord strut during the inspection required by paragraph (b) of this AD, prior to further flight, modify in accordance with the service bulletin. \n\n\t\t(2)\tIf cracking is detected in the mid-chord strut during the inspection required by paragraph (b) of this AD, prior to further flight, repair in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. \n\n\t(c)\tIf cracking is detected during the inspection required by paragraph (a) of this AD, prior to further flight, remove the stiffener straps from the mid-chord of the inboard and outboard sides of the strut, and perform an open hole eddy current inspection to detect cracking of the fastener holes in the mid-chord, in accordance with Boeing Service Bulletin 757-54-0028, dated March 31, 1994. \n\n\t\t(1)\tIf no cracking is detected in the mid-chord strut during the inspection required by paragraph (c) of this AD, prior to further flight, modify in accordance with the service bulletin. \n\n\t\t(2)\tIf cracking is detected in the mid-chord strut during the inspection required by paragraph (c) of this AD, prior to further flight, repair in accordance with a method approved by the Manager, Seattle ACO, FAA, Transport Airplane Directorate. \n\n\t(d)\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: 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(e)\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(f)\tThe inspections, strap removal, and modification shall be done in accordance with Boeing Service Bulletin 757-54-0028, 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(g)\tThis amendment becomes effective on July 21, 1994.

Recently, the FAA received a report from an operator that cracking was found in the lower spar chord of a strut on a Boeing Model 757 series airplane equipped with a Rolls Royce Model RB211-535 series engine. This cracking penetrated through the inboard flange of the chord and propagated into the skin flange of the chord. This fatigue crack in the skin flange was approximately five inches in length. \n\n\tAnalysis indicates that stiffener straps, which were installed on early production airplanes, increase the likelihood of cracking in the spar chords. These stiffener straps are no longer installed on later production airplanes. \n\n\tContinued operation with the stiffener straps installed will cause fatigue cracking or propagation of existing cracks in the lower chord. Such cracking could result in the inability of the strut to carry required engine support loads, and ultimately could lead to separation of the engine from the strut. \n\n\tThe FAA has reviewed and approved Boeing Service Bulletin 757-54-0028, dated March 31, 1994, that describes procedures for eddy current inspection to detect cracking of the lower spar chord of the engine strut, removal of the stiffener straps from the mid-chord, open hole eddy current inspection of the fastener holes, and modification. This modification, which includes installing fasteners, a strut pneumatic duct, a fire extinguisher line, a bulkhead coverplate, and a panel, will decrease the likelihood of fatigue cracking in the lower spar chord of the engine strut. \n\n\tSince an unsafe condition has been identified that is likely to exist or develop on other Boeing Model 757 series airplanes of the same type design, this AD is being issued to prevent cracking of the lower spar chord of the engine strut. This AD requires eddy current inspection to detect cracking of the lower spar chord of the engine strut, removal of the stiffener straps from the mid-chord, open hole eddy current inspection of the fastener holes, and modification. The actions are required to be accomplished in accordance with the service bulletin described previously. In certain cases, this AD requires repair of cracking in accordance with an FAA-approved method. \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 of the 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 thefollowing statement is made: "Comments to Docket Number 94-NM-85-AD." The postcard will be date stamped and returned to the commenter. \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 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 thatthis 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\n List 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: PART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1.\tThe authority citation for 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: