AD 94-07-06

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that requires inspections to detect cracked or fractured H-11 steel bolts, replacement of discrepant bolts with ones made of Inconel 718 material, and eventual replacement of all H-11 steel bolts installed at certain critical locations with Inconel 718 material bolts. This amendment is prompted by reports of cracked and fractured H-11 steel bolts installed at certain critical locations of the airframe structure. The actions specified by this AD are intended to prevent the failure of attachment bolts in critical locations, which could lead to severe airframe damage.

Final rule

94-07-06 BOEING: Amendment 39-8864. Docket 93-NM-150-AD. \n\n\tApplicability: Model 747 series airplanes having line numbers 641 through 708, inclusive, excluding Model 747-400 series airplanes; certificated in any category. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent severe structural damage to the airplane due to failure of attachment bolts, accomplish the following: \n\n\t(a)\tPrior to the accumulation of 4 years total time-in-service, or within 15 months after the effective date of this AD, whichever occurs later, perform a visual inspection, in accordance with Boeing Service Bulletin 747-51-2048, dated January 14, 1993, or Revision 1, dated January 27, 1994, to verify if bolts made of H-11 steel have been installed at the following locations: \n\nNOTE 1: Not all airplanes need to be inspected at each critical location. Operators should refer to the Boeing service bulletin to determine which specific locations are to be inspected onwhich airplanes. \n\n\t\t(1)\tBody landing gear inboard and outboard trunnion vertical support\n\t\t\tattachment. \n\t\t(2)\tWing landing gear beam upper chord to longeron attachment. \n\t\t(3)\tWing landing gear beam lower chord to crease beam attachment.\n \t\t(4)\tBody Station (BS) 2598 horizontal stabilizer hinge attachment. \n\t\t(5)\tBS 2598 longeron splice fitting attachment at stringers 11 and 23. \n\t\t(6)\tFin to body attachment. \n\t\t(7)\tHorizontal stabilizer front spar jack screw attachment. \n\n\t(b)\tIf no bolt made of H-11 steel is detected, no further action is required by this AD. \n\n\t(c)\tIf any bolt made of H-11 steel is detected, prior to further flight, visually inspect the bolt to detect cracking or fracture, in accordance with Boeing Service Bulletin 747-51-2048, dated January 14, 1993, or Revision 1, dated January 27, 1994. \n\nNOTE 2: A bolt made of H-11 steel is considered to be fractured if the sealant around the nut or bolthead is broken, or if there are gaps between the boltheador nut and the adjacent structure. \n\n\t\t(1)\tIf no cracking or fracture of the bolt is detected, repeat the inspection of that bolt thereafter at intervals not to exceed 18 months. \n\n\t\t(2)\tIf any cracking or fracture is detected during this inspection or during any inspection required by paragraph (c)(1) of this AD, prior to further flight, replace the discrepant bolt with a bolt made of Inconel 718 material in accordance with the service bulletin. \n\n\t(d)\tWithin 48 months after the effective date of this AD, replace all bolts made of H-11 steel installed at the locations specified in paragraph (a) of this AD with bolts made of Inconel 718 material, in accordance with Boeing Service Bulletin 747-51-2048, dated January 14, 1993, or Revision 1, dated January 27, 1994. Such replacement constitutes terminating action for the inspection requirements of this AD. \n\n\t(e)\tAn alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safetymay be used if approved by the Manager, Seattle Aircraft Certification Office (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\nNOTE 3: 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(f)\tSpecial flight permits may be issued in accordance with Federal Aviation Regulations (FAR) 21.197 and 21.199 to operate the airplane to a location where the requirements of this AD can be accomplished. \n\n\t(g)\tThe inspection and replacement shall be done in accordance with Boeing Service Bulletin 747-51-2048, dated January 14, 1993, or Boeing Service Bulletin 747-51-2048, Revision 1, dated January 27, 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(h)\tThis amendment becomes effective on May 5, 1994.

A proposal to amend part 39 of the Federal Aviation Regulations to include an airworthiness directive (AD) that is applicable to certain Boeing Model 747 series airplanes was published in the Federal Register on December 15, 1993 (58 FR 65567). That action proposed to require inspections to detect cracked or fractured H-11 steel bolts, replacement of discrepant bolts with ones made of Inconel 718 material, and eventual replacement of all H-11 steel bolts installed at certain critical locations with bolts made of Inconel 718 material. \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\n\tOne commenter supports the proposal. \n\n\tTwo commenters request that the applicability of the proposal be revised to exclude Model 747-400 series airplanes. These commenters state, and the manufacturer has confirmed, that these airplanes were delivered without H-11 steel bolts installed. The FAA concurs. Since issuance of the notice, the FAA has reviewed and approved Boeing Service Bulletin 747-51-2048, Revision 1, dated January 27, 1994, which excludes Model 747-400 series airplanes from the effectivity listing. Since these airplanes were not delivered with H-11 bolts, they are not subject to the addressed unsafe condition. The FAA has revised the final rule to exclude Model 747-400 series airplanes from the applicability, and to reference this latest revision of the service bulletin as an additional source of appropriate service information. Additionally, the FAA has revised the economic impact information, below, to reflect the exclusion of Model 747-400 series airplanes. \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 changeswill neither increase the economic burden on any operator nor increase the scope of the AD. \n\n\tThere are approximately 60 Model 747 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 7 airplanes of U.S. registry will be affected by this AD. \n\n\tIt would take an average of 15 work hours per airplane to accomplish the proposed inspection actions, at an average labor rate of $55 per work hour. Based on these figures, the total cost impact of the proposed inspection action of this AD on U.S. operators is estimated to be $5,775, or $825 per airplane, per inspection cycle. \n\n\tIt would take an average of 240 work hours per airplane to accomplish the proposed bolt replacement action, at an average labor rate of $55 per work hour. Required parts would cost approximately $11,000 per airplane. Based on these figures, the total cost impact of the proposed replacement action of this AD on U.S. operators is estimated to be $169,400, or $24,200 per airplane. (This estimate assumes that H-11 steel bolts are found at all affected locations.) Accomplishment of this replacement action terminates the repetitive inspection requirement; therefore the accomplishment of the replacement will result in a reduction in costs to affected operators of $275 per airplane per inspection cycle that will no longer be required. \n\n\tThe number of required work hours, as indicated above, is presented as if the accomplishment of the actions proposed in this AD were to be conducted as "stand alone" actions. However, in actual practice, these actions for the most part would be accomplished coincidentally or in combination with normally scheduled airplane inspections and other maintenance program tasks. Therefore, the actual number of necessary additional work hours would be minimal in many instances. Additionally, any costs associated with special airplane scheduling would be minimal. \n\n\tThe total cost impact figure discussed above is based on assumptionsthat 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 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 \nAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\nAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends 14 CFR part 39 of the Federal Aviation Regulations as follows: \n\nPART 39 - AIRWORTHINESS DIRECTIVES \n\n1.\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. \n\n§ 39.13 - (Amended) \n2.\tSection 39.13 is amended by adding the following new airworthiness directive: