AD 94-17-01 SUPERSEDED

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that requires inspections to detect cracking in the upper row of fasteners in the lower lobe of the fuselage skin lap joints, and repair, if necessary. This amendment is prompted by reports of incidents involving fatigue cracking and corrosion in transport category airplanes that are approaching or have exceeded their design life goal. The actions specified by this AD are intended to prevent separation of the fuselage skin and rapid loss of pressure in the airplane. This AD also relates to the recommendations of the Airworthiness Assurance Working Group assigned to review Model 747 series airplanes, which indicate that, to assure long term continued operational safety, various structural inspections should be accomplished.

Final rule

94-17-01 BOEING: Amendment 39-8996. Docket 93-NM-204-AD. \n\n\tApplicability: Model 747 series airplanes having line positions 1 through 200 inclusive, certificated in any category. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent separation of fuselage skin and rapid loss of pressure in the airplane, accomplish the following: \n\n\t(a)\tPerform an external high frequency eddy current inspection to detect cracks in the upper row of fasteners in the modified lap joints in accordance with Boeing Service Bulletin 747- 53A2267, Revision 3, dated March 26, 1992, at the time specified in paragraph (a)(1) or (a)(2) or (a)(3) of this AD, as applicable. \n\n\t\t(1)\tFor airplanes on which the full modification required by AD 90-06-06, Amendment 39-6490, has been accomplished in accordance with Revision 2 of Boeing Service Bulletin 747-53A2267, dated March 29, 1990, or Revision 3, dated March 26, 1992: Prior to the accumulation of 10,000 flight cycles after accomplishment of the full modification. \n\n\t\t(2)\tFor airplanes on which the full modification required by AD 90-06-06, Amendment 39-6490, has been accomplished in accordance with Boeing Service Bulletin 747- 53A2267, dated March 28, 1986, or Revision 1, dated September 25, 1986: Prior to the accumulation of 7,000 flight cycles after accomplishment of the full modification. \n\n\t\t(3)\tFor airplanes on which the optional modification has been accomplished in accordance with Boeing Service Bulletin 747-53A2267, Revision 2, dated March 29, 1990; or Revision 3, dated March 26, 1992: Prior to the accumulation of 7,000 flight cycles after accomplishment of the optional modification. \n\n\t(b)\tIf no cracking is detected, repeat the inspection required by paragraph (a) of this AD thereafter at intervals not to exceed 3,000 flight cycles. \n\n\t(c)\tIf any cracking is detected, prior to further flight, repair in accordance with the Section 53-30-03 of the 747 Structural Repair Manual (SRM), and repeat the inspections required by paragraph (a) of this AD. \n\n\t\t(1)\tIf the repair specified in the 747 SRM does not include removing the lap joint and the upper row of countersunk fasteners, thereafter at intervals not to exceed 3,000 flight cycles. \n\t\t(2)\tIf the repair specified in the 747 SRM includes removing the lap joint and the upper row of countersunk fasteners, such repair constitutes terminating action for the inspection requirements of this AD. \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, maybe 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 shall be done in accordance with Boeing Service Bulletin 747-53A2267, Revision 3, dated March 26, 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 14, 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 14, 1994 (59 FR 11733). That action proposed to require repetitive external high frequency eddy current inspections (HFEC) to detect cracking in the upper row of fasteners in the lower lobe of the fuselage skin lap joints, and repair, if necessary. \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 requests that the requirements of the proposal be revised to coincide with the actions specified in the service bulletin that is referenced in the proposal as the appropriate source of service information. The commenter states that Boeing Service Bulletin 747-53A2267, Revision 3, dated March 26, 1992, excludes airplanes on which lap joints are thicker than 0.071 inch. The FAA does not concur. The FAA finds that the requirements of the AD and the actions specified in Revision 3 of the service bulletin include inspection of areas at the upper row of fasteners in the lap joint on which the thickness of the skin is 0.090 inch or less (where protruding head fasteners are required). As such, airplanes on which the skin of the lap joints is thicker than 0.071 inch are not exempt from the requirements of the AD or the actions specified in the referenced service bulletin. \n\n\tOne commenter questions the justification for including the airplane having line position 1 in the applicability of the proposal since it is not included in the effectivity of Boeing Service Bulletin 747-53A2267, Revision 3, dated March 26, 1992, which is referenced in the proposal as the appropriate source of service information. From this comment, the FAA infers that the commenter requests that this airplanebe deleted from the applicability of the proposal. The FAA does not concur. The FAA intentionally included airplane having line position 1 in the applicability of the rule since it, too, is subject to the same unsafe condition as those airplanes listed in the referenced service bulletin. Therefore, no change to the final rule is necessary. \n\n\tOne commenter requests that the proposal be revised to include specific procedures to accomplish the inspection required by paragraph (a) for airplanes that have been modified to install a main deck side cargo door (MDSCD) in accordance with a supplemental type certificate (STC). The commenter states that, as a result of the STC modification, the MDSCD doublers cover the lap joints. The FAA does not concur. The FAA's intent is not to address in this rule every conceivable airplane configuration for every operator. Consequently, paragraph (d) of this AD provides for FAA approval of alternative methods of compliance to address unique circumstances. Until such time that the FAA approves of such alternative methods of compliance, operators are required to remove the doublers that cover the lap joints to accomplish the required inspection. Therefore, no change to the final rule is necessary. \n\n\tOne commenter requests correction of typographical errors in the applicability statements of proposed paragraphs (a)(2) and (a)(3). The commenter notes that the correct date for the original issue of Boeing Service Bulletin 747-53A2267 is March 28, 1986, rather than March 8, 1986, as erroneously referenced in paragraph (a)(2) of the proposal. This commenter also points out that the optional modification referenced in the applicability statement of proposed paragraph (a)(3) is in error. The optional modification was not introduced until Revision 2 of the service bulletin; therefore, the reference to the original issue and Revision 1 of the service bulletin in proposed paragraph (a)(3) is erroneous. The FAA concurs. Paragraphs (a)(2) and (a)(3) of the final rule have been revised accordingly. \n\n\tOne commenter requests clarification of the requirement in proposed paragraph (c) to inspect following repair of the lap joint in accordance with the 747 Structural Repair Manual (SRM) since the SRM specifies various repairs depending upon the extent of damage to the lap joint. The FAA concurs that clarification is warranted. The FAA finds that if the damage to the lap joint is such that the repair specified in the SRM includes removing the lap joint and the upper row of countersunk fasteners, then the inspection required by paragraph (a) of the final rule does not have to be repeated following such repairs. Paragraph (c) of the final rule has been revised accordingly. \n\n\tOne commenter requests that detailed visual inspections of the lap joints to detect corrosion be included in the proposal, in light of the consequences of crack propagation due to corrosion in lap joints. The commenter notes that these inspections are specified in Boeing Service Bulletin 747-53A2267, which is referenced in the proposal as the appropriate source of service information. The FAA concurs, in part. The FAA acknowledges the criticality of inspecting to detect corrosion. However, as stated in the proposal, these inspections are currently required by AD 90-25-05, Amendment 39-6790 (55 FR 49268, November 27, 1990), which requires inspections to detect fatigue cracking due to corrosion. Therefore, no change to the final rule is necessary. \n\n\tAnother commenter, a non-U.S. operator, requests that the proposed rule be revised to include a provision specifying that pressurization cycles of 2.0 psi or less need not be counted as a flight cycle when determining the number of flight cycles relative to the proposed compliance thresholds. \n\n\tThe FAA does not concur. The FAA considers it inappropriate to include various provisions in an AD applicable to a single operator's unique use of an affected airplane. Paragraph (d) of this AD provides for the approval of alternative methods of compliance to address these types of unique circumstances. Further, this commenter does not compile data for each of its airplanes so that an individual airplane's pressurization cycles could be determined; instead, it uses a fleet average to calculate the equivalent number of pressurization cycles. The FAA does not consider it appropriate to use approximations for determining compliance with this AD. \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 changes will neither increase the economic burden on any operator nor increase the scope of the AD. \n\n\tThere are approximately 200 Model 747 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 118 airplanes of U.S. registry will be affected by this AD, that it will take approximately 124 work hours per airplane to accomplish the required actions, and that the average labor rate is $55 per work hour. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $804,760, or $6,820 per airplane. \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 FAA recognizes that the required inspections will require a large number of work hours to accomplish. However, the compliance times specified in paragraph (a) of this AD should allow ample time for the inspections to be accomplished coincidentally with scheduled major airplane inspection and maintenance activities, thereby minimizing the costs associated with special airplane scheduling. \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 underthe 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:\n\n 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.