AD 97-08-08

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 777-200 series airplanes. This action requires repetitive visual inspections of the forward mounts of certain engines to detect damaged, missing, or failed parts, and eventual modification of those engines. Accomplishment of this modification terminates the requirement for repetitive inspections. This amendment is prompted by a report indicating that bolts that attach the yoke of the forward mount to the fan case of the engine have failed due to fatigue cracking. The actions specified in this AD are intended to prevent fatigue cracking in these bolts, which could lead to failure of these bolts and consequent separation of the engine from the wing.

Final rule; request for comments

97-08-08 BOEING: Amendment 39-9996. Docket 97-NM-60-AD. \n\n\tApplicability: Model 777-200 series airplanes powered by General Electric (GE) 90 engines having serial number 900-104, -105, -106, -108, -109, -110, or -111; 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 (c) 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 addressit. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent fatigue cracking in the bolts that attach the yoke of the forward mount of the engine to the fan case of the engine, which could lead to failure of these bolts and consequent separation of the engine from the wing, accomplish the following: \n\n\t(a)\tFor airplanes powered by GE90 engines having serial numbers 900-105 and -110: \n\n\t\t(1)\tWithin 125 landings after the effective date of this AD, conduct a visual inspection of the yoke of the forward mount of the engine to detect damaged, missing, or failed attachment bolts, or failed engine mount links, in accordance with GE Aircraft Engines Service Bulletin 72-183, dated February 28, 1997. \n\n\t\t\t(i)\tIf no discrepancy is found, repeat this inspection thereafter at intervals not to exceed 125 landings. \n\n\t\t\t(ii)\tIf any discrepancy is found, prior to further flight, modify the engine in accordance with GE Aircraft Engines Service Bulletin 72-275,dated March 4, 1997. No further action is required by this AD for that engine. \n\n\t\t(2)\tWithin 1,000 landings after the effective date of this AD, modify the engine in accordance with GE Aircraft Engines Service Bulletin 72-275, dated March 4, 1997. Accomplishment of this modification constitutes terminating action for the repetitive inspections of that engine required by paragraph (a)(1)(i) of this AD. \n\n\t(b)\tAs of the effective date of this AD, no operator shall install on any airplane any GE90 engine having serial number 900-104, 900-106, 900-108, 900-109, or 900-111 unless that engine has been modified in accordance with GE Aircraft Engines Service Bulletin 72-275, dated March 4, 1997. \n\n\t(c)\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(d)\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(e)\tThe inspections and modification shall be done in accordance with GE Aircraft Engines Service Bulletin 72-183, dated February 28, 1997, and GE Aircraft Engines Service Bulletin 72-275, dated March 4, 1997. 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 General Electric Aircraft Engines, GE90 Product Support, One Neuman Way, Cincinnati, Ohio 45215-6301. 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(f)\tThis amendment becomes effective on May 7, 1997.

During certification testing of the General Electric (GE) 90 engine, fatigue cracking was detected in the bolts that attach the yoke of the forward mount of the engine to the fan case of the engine. Fatigue cracking in the bolts that attach the yoke of the forward mount of the engine to the fan case of the engine, if not prevented, could lead to failure of these bolts and consequent separation of the engine from the wing. \n\n\tAn analysis revealed that these bolts had a short fatigue life due to the large forces that the yoke exerted on them. As a result, the original yoke design was not certified as meeting the damage tolerance standards of part 25 of the Federal Aviation Regulations (14 CFR part 25). The engine manufacturer subsequently redesigned the yoke and fan case to those standards in order to prevent fatigue cracking in the bolts.\n\n\tAlthough the airplane manufacturer did not install GE90 engines with the original yoke design on any Model 777-200 series airplanes, the engine manufacturer shipped some of these engines to operators as replacement engines. The engine manufacturer had apparently concluded, in error, that if the yoke complied with the strength requirements of part 33 of the Federal Aviation Regulations (14 CFR part 33), it could ship engines containing yokes of the original design for use as spare engines for these airplanes. The yoke must, in fact, meet both the strength standards of part 33 and the damage tolerance standards of part 25 in order to be certificated for installation on the Boeing Model 777-200 series airplane. The discrepant yokes are installed in GE90 engines having serial numbers 900-104, -105, -106, -108, -109, -110, and -111.\n\n Explanation of Relevant Service Information \n\n\tThe FAA has reviewed and approved GE Aircraft Engines Service Bulletin 72-183, dated February 28, 1997, which describes procedures for conducting a visual inspection of the yoke of the forward mount of certain GE90engines to detect damaged, missing, or failed attachment bolts, or failed engine mount links. \n\n\tThe FAA also has reviewed and approved GE Aircraft Engines Service Bulletin 72-275, dated March 4, 1997, which describes procedures for modifying GE90 engines by replacing the yoke of the forward engine mount with a new yoke. The new yoke has been redesigned so that it meets the damage tolerance standards of part 25 of the Federal Aviation Regulations (14 CFR part 25), and will preclude fatigue cracking in the bolts that attach the yoke to the fan case of the engine. Accomplishment of this replacement will eliminate the need for visual inspections of the yoke area. \n\nExplanation of Requirements of 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 prevent fatigue cracking in the bolts that attach the yoke of the forward mount of the engine to the fan case of the engine, which could lead to failure of these bolts and consequent separation of the engine from the wing. This AD requires repetitive visual inspections of the yoke of the forward mounts of certain GE90 engines to detect damaged, missing, or failed attachment bolts, or failed engine mount links; and eventual modification of those engines. Accomplishment of the modification terminates the requirement for visual inspections of the yoke. The actions are required to be accomplished in accordance with the service bulletins described previously. \n\nCost Impact \n\n\tNo Model 777-200 series airplane powered by the General Electric 90 engines affected by this action is on the U.S. Register. All airplanes included in the applicability of this rule currently are operated by non-U.S. operators under foreign registry; therefore, they are not directly affected by this AD action. However, the FAA considers that this rule is necessary to ensure that the unsafe condition is addressed in the event that any of these subject airplanes are imported and placed on the U.S. Register in the future. \n\n\tShould an affected airplane be imported and placed on the U.S. Register in the future, it would require approximately 1 work hour to accomplish the required inspection, at an average labor charge of $60 per work hour. Based on these figures, the cost impact of the required inspection of this AD would be $60 per airplane. \n\n\tAdditionally, it would require approximately 72 work hours to accomplish the required modification, at an average labor charge of $60 per work hour. Required parts would be supplied by the manufacturer at no cost to operators. Based on these figures, the cost impact of the required modification of this AD would be $4,320 per airplane. \n\nDetermination of Rule's Effective Date \n\n\tSince this AD action does not affect any airplane that is currently on the U.S. register, it has no adverse economic impact and imposes no additional burden on any person. Therefore, prior notice and public procedures hereon are unnecessary and the amendment may be made effective in less than 30 days after publication in the Federal Register. \n\nComments Invited \n\n\tAlthough this action is in the form of a final rule and was not preceded by notice and 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 the following statement is made: "Comments to Docket Number 97-NM-60-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\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: 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: