AD 94-15-17 ACTIVE

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that requires inspections to detect cracking of certain fuselage longitudinal lap joints, repair of any cracking found, and replacement of the countersunk fasteners in those lap joints with protruding head fasteners. This amendment is prompted by a structural reassessment of Model 747 series airplanes. The actions specified by this AD are intended to prevent skin cracking in the longitudinal lap joints of certain stringers, which can lead to rapid decompression of the airplane.

Final rule

94-15-17 BOEING: Amendment 39-8988. Docket 93-NM-212-AD. \n\n\tApplicability: Model 747 series airplanes, having line numbers 201 through 230 inclusive; certificated in any category. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent rapid decompression of the airplane, accomplish the following: \n\n\t(a)\tPrior to the accumulation of 15,000 total flight cycles or within 1,000 flight cycles after the effective date of this AD, whichever occurs later, perform an external high frequency eddy current (HFEC) inspection to detect cracking of the skin at the upper row of countersunk fasteners in the longitudinal lap joints of Stringer (S-)12L and S-12R from station 520 to station 741.1, in accordance with Boeing Service Bulletin 747-53-2366, dated August 6, 1992. \n\n\t\t(1)\tIf no cracking is found, repeat the inspection thereafter at intervals not to exceed 4,000 flight cycles until the replacement of fasteners required by paragraph (b) of this AD is accomplished. \n\n\t\t(2)\tIf any cracking is found, prior to further flight, repair in accordance with the 747 Structural Repair Manual. After repair, repeat the inspection at intervals not to exceed 4,000 flight cycles until the replacement of fasteners required by paragraph (b) of this AD is accomplished. \n\n\t(b)\tPrior to the accumulation of 20,000 total flight cycles or within 4 years after the effective date of this AD, whichever occurs later, replace the countersunk fasteners in the upper row of the longitudinal lap joints of S-12L and S-12R from station 520 to station 741.1 with protruding head fasteners, in accordance with Boeing Service Bulletin 747-53-2366, dated August 6, 1992. Replacement of these fasteners constitutes terminating action for the repetitive inspections required by paragraph (a) of this AD. \n\n\t(c)\tPrior to the accumulation of 10,000 total flight cycles after replacement of the countersunk fasteners required by paragraph (b) of this AD, perform an external HFEC inspection to detect cracking of the skin at the upper row of protruding head fasteners in the longitudinal lap joints of S-12L and S-12R from station 520 to station 741.1, in accordance with Boeing Service Bulletin 747-53-2366, dated August 6, 1992. \n\n\t\t(1)\tIf no cracking is found, repeat the inspection thereafter at intervals not to exceed 3,000 flight cycles. \n\n\t\t(2)\tIf any cracking is found, prior to further flight, repair in accordance with the 747 Structural Repair Manual. After repair, repeat the inspection at intervals not to exceed 3,000 flight cycles. \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 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: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 and replacement shall be done in accordance with Boeing Service Bulletin 747-53-2366, including the "ADDENDUM," dated August 6, 1992. 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 September 2, 1994.

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 747 series airplanes was published in the Federal Register on March 4, 1994 (59 FR 10338). That action proposed to require repetitive external high frequency eddy current inspections to detect cracking of the skin around the fasteners in the upper row of the longitudinal lap joints of Stringer (S)-12L and S-12R from station 520 to station 741.1, repair of any cracking found, and replacement of the countersunk fasteners in those lap joints with protruding head fasteners. \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\tTwo commenters support the proposed rule. \n\n\tOne commenter requests that the compliance time specified in proposed paragraph (b) for accomplishing the replacement of the countersunk fasteners be reduced from the proposed "20,000 total flight cycles or within 4 years after the effective date of the AD, whichever occurs later," to "20,000 total flight cycles or within 2 years after the effective date of the AD, whichever occurs later." The commenter states that this suggested shorter compliance time would make the compliance time requirements of the proposed AD commensurate with the compliance time of AD 94-12-09, amendment 39-8937 (59 FR 30285, June 13, 1994), which requires modification of certain skin panel lap joints in this same area. \n\n\tThe FAA does not concur. After consideration of all the available information, the FAA cannot conclude that a reduction of the proposed compliance time, without prior notice and opportunity for public comment, is warranted. In developing an appropriate compliance time, the FAA considered the safety implications, parts availability, and normal maintenance schedules for timely accomplishment of replacement of the fasteners. Further, the proposed compliance time was arrived at with operator, manufacturer, and FAA concurrence. In consideration of all of these factors, the FAA determined that the compliance time, as proposed, represents an appropriate interval in which replacement of the fasteners can be accomplished in a timely manner within the fleet and still maintain an adequate level of safety. Operators are always permitted to accomplish the requirements of an AD at a time earlier than that specified as the compliance time; therefore, if an operator elects to accomplish the fastener replacement prior to the accumulation of 20,000 total flight cycles or 2 years after the effective date of this AD, whichever is later (in order to accomplish the replacement concurrently with an action required by another AD), it is that operator's prerogative to do so. If additional data are presented that would justify a shorter compliance time, the FAA may consider further rulemaking on this issue. \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 as proposed. \n\n\tThere are approximately 30 Model 747 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 12 airplanes of U.S. registry will be affected by this AD, that it will take approximately 17 work hours per airplane to accomplish the required inspections, and that the average labor rate is $55 per work hour. Based on these figures, the total cost impact of the required inspections on U.S. operators is estimated to be $11,220, or $935 per airplane. \n\n\tThe FAA estimates that it will take approximately 302 work hours per airplane to accomplish the requirement to replace fasteners, and that the average labor rate is $55 per work hour. Required parts will be nominal in cost. Based on these figures, the total cost impact of the requirement to replace fasteners on U.S. operators is estimated to be $199,320, or $16,610 per airplane. \n\n\tBased on the figures, above, the total cost impact of the required actions (cost of inspections added to the cost of replacement of fasteners) on U.S. operators is estimated to be $210,540, or $17,545 per airplane.\n \n\tThe FAA recognizes that the replacement of fasteners would require a large number of work hours to accomplish. However, the 4-year compliance time specified in paragraph (b) of this AD should allow ample time for the replacement of the fasteners to be accomplished coincidentally with scheduled major airplane inspection and maintenance activities, thereby minimizing the costs associated with special airplane scheduling. \n\n\tThe total 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. \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 thelocation 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:

The service information referenced in this AD may be obtained from Boeing\nCommercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. This information may be examined at the Federal Aviation Administration (FAA), Transport Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Steven C. Fox, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (206) 227-2777; fax (206) 227-1181.