AD 99-07-12

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747-100, -200, and -300 series airplanes, that requires repetitive inspections to detect cracking of certain lower lobe fuselage frames, and repair, if necessary. This amendment is prompted by reports indicating that fatigue cracks were found in lower lobe frames on the left side of the fuselage. The actions specified by this AD are intended to detect and correct fatigue cracking of certain lower lobe fuselage frames, which could lead to fatigue cracks in the fuselage skin, and consequent rapid decompression of the airplane.

Final rule

99-07-12 BOEING: Amendment 39-11097. Docket 97-NM-87-AD. \n\n\tApplicability: Model 747-100, -200, and -300 series airplanes, as listed in Boeing Alert Service Bulletin 747-53A2408, dated April 25, 1996; 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 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 (e) 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 address it. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo detect and correct fatigue cracking of certain lower lobe fuselage frames, which could lead to fatigue cracks in the fuselage skin, and consequent rapid decompression of the airplane, accomplish the following: \n\n\tNOTE 2: Although Boeing Alert Service Bulletin 747-53A2408, dated April 25, 1996, allows discount from the compliance threshold of all flight cycles at or below a cabin pressure differential of 2.0 pounds per square inch (psi), this AD requires that all flight cycles be counted. \n\n\t(a)\tFor airplanes on which the initial detailed visual internal inspection of the Section 46 lower lobe frames required by paragraph (a)(3) of AD 93-08-12, amendment 39-8559, has not been accomplished: Perform a detailed visual inspection to detect cracking of the lower lobe fuselage frames from Body Station 1820 to Body Station 2100, in accordance with Boeing Alert Service Bulletin 747-53A2408, dated April 25, 1996, at the later of thetimes specified in paragraphs (a)(1) and (a)(2) of this AD: \n\n\t\t(1)\tPrior to the accumulation of 15,000 total flight cycles; or \n\n\t\t(2) Within 1,500 flight cycles or 18 months after the effective date of this AD, whichever occurs first. \n\tNOTE 3: Paragraph (a)(3) of AD 93-08-12 requires a detailed visual internal inspection to detect cracks in the Section 46 lower lobe frames, in accordance with Boeing Service Bulletin 747-53-2349, dated June 27, 1991. The initial inspection is required prior to the accumulation of 22,000 total flight cycles, or within 1,000 flight cycles after June 11, 1993 (the effective date of AD 93-08-12), whichever occurs later. \n\nRepetitive Inspections \n\n\t(b)\tIf no cracking is detected during the inspection required by paragraph (a) of this AD, repeat the inspection thereafter at intervals not to exceed 3,000 flight cycles. \n\nCorrective Actions \n\n\t(c)\tIf any cracking is detected during any inspection required by paragraph (a) of this AD, prior tofurther flight, accomplish paragraphs (c)(1) and (c)(2) of this AD: \n\n\t\t(1)\tWithin 20 inches of the crack location on the frame, perform a detailed visual inspection of the adjacent structure to detect cracking. If any cracking is detected, prior to further flight, repair in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate; the Boeing 747 Structural Repair Manual; or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative who has been authorized by the Manager, Seattle ACO, to make such findings. \n\n\t\t(2)\tRepeat the inspection required by paragraph (a) of this AD thereafter at intervals not to exceed 3,000 flight cycles. \n\nOptional Terminating Inspection \n\n\t(d)\tAccomplishment of the initial detailed visual internal inspection of the Section 46 lower lobe frames required by paragraph (a)(3) of AD 93-08-12 constitutes terminating action for the requirements of this AD. \n\nAlternative Methods of Compliance \n\n\t(e)\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 4: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO. \n\nSpecial Flight Permits \n\n\t(f)\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\nIncorporation by Reference \n\n\t(g)\tExcept as provided by paragraphs (c)(1) and (d) of this AD, the actions shall be done in accordance with Boeing Alert Service Bulletin 747-53A2408, dated April 25, 1996. 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, 1999.

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 747-100, -200, and -300 series airplanes was published in the Federal Register on August 4, 1998 (63 FR 41483). That action proposed to require repetitive inspections to detect cracking of certain lower lobe fuselage frames, and repair, if necessary. \n\nComments Received \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\nSupport for the Proposed Rule \n\n\tTwo commenters support the proposed rule. \n\nRequest to Increase the Threshold and Allow Discounting of Flights Below 2.0 PSI \n\n\tOne commenter requests that the proposed AD be revised to reflect the threshold of 16,000 flight cycles, as recommended in Boeing Alert Service Bulletin 747-53A2408, dated April 25, 1996 (which is referenced in the proposed AD as the appropriate source of service information for accomplishment of the required actions), and to allow discounting of flight cycles less than 2.0 pounds per square inch (psi). The commenter states that the critical crack is not a severed frame, but a severed frame with a skin crack. The commenter further states that there were no reports of skin cracking associated with the cracked frames, and that analysis shows that an existing skin crack at a severed frame will not grow to critical length prior to the inspection threshold identified in the referenced service bulletin. In addition, the fleet reports used in this analysis were adjusted to account for flights less that 2.0 psi. \n\n\tThe FAA does not concur with the commenter's request. As discussed under the heading "Differences Between the Proposed AD and Relevant Service Bulletin" in the preamble of the proposed AD, the FAA has received a report of cracking (i.e., a completely severed frame,consisting of the frame web, inner chord, and fail-safe chord) on an airplane that had accumulated only 15,227 total flight cycles. As a result, the FAA determined that a compliance threshold of 15,000 total flight cycles for initiating the required actions is warranted, in that it represents an appropriate interval of time allowable for affected airplanes to continue to operate without compromising safety. \n\n\tIn the same regard, the FAA does not find that allowing the discount of flight cycles below 2.0 psi would adequately address the unsafe condition. The FAA has received a report of two adjacent frames being completely severed on an airplane that had accumulated 12,817 full pressure cycles, plus 8,761 cycles at less than 2.0 psi differential pressure. As stated in the NPRM, this reported cracking is more indicative of the reported findings on airplanes that had accumulated 20,000 total flight cycles. If the FAA allowed the discount of flight cycles below 2.0 psi, as recommended in the referenced service bulletin, the identified unsafe condition on that airplane would go undetected for several thousand flight cycles. Therefore, the FAA finds that no change to the final rule is necessary. \n\nExplanation of Changes Made to the Proposal \n\n\tThe FAA has revised paragraph (c)(1) of the final rule to also allow repair of any crack in the subject area to be accomplished in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative who has been authorized by the FAA to make such findings. \n\nConclusion \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 change previously described. The FAA has determined that the change will neither increase the economic burden on any operator nor increase the scope of the AD. \nInterim Action \n\n\tThis is considered to be interim action until the accomplishment of AD 93-08-12, amendment 39-8559 (58 FR 27927, May 12, 1993). That AD requires a detailed visual internal inspection to detect cracks in the Section 46 lower lobe frames, and repair, if necessary, in accordance with Boeing Service Bulletin 747-53-2349, dated June 27, 1991. The initial inspection required by AD 93-08-12 is required prior to the accumulation of 22,000 total flight cycles. The FAA now finds that earlier inspection (i.e., prior to accumulation of 15,000 total flight cycles) of the lower lobe frames is warranted, as required by this AD. \n\nCost Impact \n\n\tThere are approximately 452 Model Boeing 747-100, -200, and -300 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 152 airplanes of U.S. registry will be affected by this AD, that it will take approximately 2 work hours per airplane to accomplish the required inspection, and that the average labor rate is $60 per work hour. Based on these figures, the cost impact of the inspection required by this AD on U.S. operators is estimated to be $18,240, or $120 per airplane, per inspection cycle. \n\n\tThe 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\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: