RULES and REGULATIONS

DEPARTMENT OF TRANSPORTATION Federal Aviation Administration 14 CFR Part 39 [Docket No. 90 -NM -210 -AD; Amendment 39 - 6997] Airworthiness Directives; Boeing Model 747 Series Airplanes Wednesday, May 15, 1991 AGENCY: Federal Aviation Administration (FAA), DOT. ACTION: Final rule. SUMMARY: This amendment supersedes an existing airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, which currently requires repetitive inspections for cracking of the frame structure and skin in the fuselage section 41 and repair, if necessary. Such cracking, if not corrected, could result in sudden decompression of the fuselage. This amendment eliminates the X-ray inspe ction option for all airplanes, eliminates the bores cope inspection for all airplanes that have accumulated more than 20,000 flight cycles, reduces the repetitive inspection intervals in certain areas, and eliminates deferral of crack repair. This amendment is prompted by recommendations of the FAA- sponsored Boeing Model 747 Structures Working Group. EFFECTIVE DATE: June 24, 1991. ADDRESSES: The applicable service information may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124. This information may be examined at the FAA, Northwest Mountain Region, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington. FOR FURTHER INFORMATION CONTACT: Mr. Steven C. Fox, Seattle Aircraft Certification Office, Airframe Branch, ANM - 120S; telephone (206) 227 -2777. Mailing address: FAA, Northwest Mountain Region, 1601 Lind Avenue SW., Renton, Washington 98055 -4056. SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal Aviation Regulationsby superseding AD 86 -23 -06 R1, Amendment 39 - 5583 ( 52 FR 7567 , March 12, 1987), applicable to Bo eing Model 747 series airplanes, to require repetitive inspections for cracking of body frames and skin in the fuselage section 41 and repair, if necessary, was published in the Federal Register on January 10, 1991 ( 56 FR 9 68 ). Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. Two commenters, the manufacturer and the Air Line Pilots Association (ALPA), fully supported the proposed rule. Another commenter, the Air Transport Association (ATA) of America on behalf of its members, expressed no ob

jection to the deletion of the x-ray and borescope inspections for airplanes with greater than 20,000 flight cycles; however, two mem bers requested that the proposed rule be revised to defer repair of cracks at body station (BS) 400 bulkhead and at the nose wheel well forward canted bulkhead, as permitted by the existing AD 86 -23 -06 R1, since these areas have been safely monitored since 1973. The FAA does not concur. Since the issuance of that AD, the FAA has determined that the areas adjacent to the frames, such as the skin panels from BS 360 to 540, stringers 6 to 14, the nose wheel well vertical beams and webs, and BS 256 canted bulkhead chords and fuselage skin, are also prone to cracking and are the subject of other AD's. Based upon these findings of cracks in the adjacent areas, the FAA has determined that, in order to assure the continued operational safety of these airplanes, deferral of repairs of known cracks cannot be permitted. Paragraph F. of the final rule has been revised to specify the current procedure for submitting requests for approval of alternative methods of compliance. The economic analysis paragraph, below, has been revised to increase the specified hourly labor rate from $40 per manhour (as was cited in the preamble to the Notice) to $55 per manhour. The FAA has determined that it is necessary to increase this rate used in calculating the cost impact asso ciated with AD activity to account for various inflationary costs in the airline industry. After 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 significantly increase the economic burden on any operator nor increase the scope of the rule. There are approximately 685 Model 747 series airplanes of the affected design in the worldwide fleet. It is estimated that 202 airplanes of U.S. registry will be affected by this AD, that it will take approximately 3,612 manhours per airplane to accomplish the required actions, and that the average labor cost will be$55 per manhour. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to

be $40,129,320. Itshould be noted that the total cost impact figure indicated above includes the labor costs of approximately 2,400 manhours for previously-required inspections that continue to be required by this new AD action. The additional costs imposed by new requirements of this AD action include labor charges for approximately 1,200 additional manhours. The 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 im plications to warrant the preparation of a Federalism Assessment. For the reasons discussed above, I certify that this action (1) is not a “major rule” under Executive Order 12291 ; (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 is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket. List of Subjects in 14 CFR Part 39 Air transportation, Aircraft, Aviation safety, Safety. Adoption of the Amendment Accordingly, 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: PART 39

—[AMENDED] 1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 1354(a), 1421 and 1423; 49 U.S.C. 106(g) (Revised Pub. L. 97 -449, January 12, 1983); and 14 CFR 11.89. 14 CFR § 39.13§ 39.13 [Amended]

14 CFR § 39.13 2. Section 39. 13 is amended by superseding amendment 39 - 5583 (52 FR 7567 , March 12, 1987), AD 86 - 23 -06 R1, with the following new airworthiness directive: AD 91 - 11 -01. Boeing: Amendment 39 - 6997. Docket No. 90 -NM -210 -AD. Supersedes AD 86 -23 -06 R1. Applicability: Model 747 series airplanes, listed in Boeing Alert Service Bulletin 747 - 53A2265, Revision 7, dated January 25, 1990, certificated in any category. Compliance: Required as indicated, unless previously accomplished. To prevent sudden decompression of the fuselage, accomplish the following: A. Within the next 500 flight cycles after the effective date of this AD, or prior to accumulating the flight limit spe cified in Boeing Drawing 624U0001, Sheet 3, Revision A, dated December 14, 1989, whichever occurs later, ac complish the inspections contained in Boeing Alert Service Bulletin 747 - 53A2265, Revision 7, dated January 25, 1990. Repeat these inspections at intervals not to exceed those specified in the drawing. B. If any cracking is found, repair in accordance with FAA-approved procedures prior to further flight. Concurrent with performing any repair, visually inspect adjacent structures in accordance with Section III of Boeing Alert Service Bulletin 747 - 53A2265, Revision 7, dated January 25, 1990, and repair any cracks in accordance with FAA-approved procedures prior to further flight. C. For the purpose of complying with this AD, the number of landings may be determined to equal the number of pressurization cycles where the cabin differential pressure was greater than 2.0 PSI. D. For Model 747SR airplanes only, based on continued mixed operation of lower cabin differentials, the initial inspection thresholds and the repetitive inspection intervals specified in this AD may be multiplied by a 1.2 adjustment factor. E. For structure that has been installed during previous airplane modification/repair, the inspection thresholds referenced in paragraph A of this AD are measured from the time of replacement of that structure. F. An alternative method of compliance or adjustment of the compliance time, which provides an ac-ceptable level of safety, may be used when approved by the Manager, Seattle Aircraft Certification Office

(ACO), FAA, Transport Airplane Directorate. Note: The request should be forwarded through an FAA Principal Maintenance Inspector, who may concur or com

ment and then send it to the Manager, Seattle ACO. G. Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes to a base in order to comply with the requirements of this AD. H. Installation of new and improved body frame structure in accordance with FAA-approved procedures or Boeing Service Bulletin 747 - 53 -2272, dated January 12, 1987, is considered terminating action for the repetitive inspections required by this AD for the structure replaced and other adjacent structure (considered to be stingers, clips, and skin associated with the frame). All persons affected by this directive who have not already received the appropriate service documents from the manuf

acturer may obtain copies upon request to Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124. These documents may be examined at the FAA, Northwest Mountain Region, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington. This amendment supersedes Amendment 39 - 5583, AD 86 -23 -06 R1. This amendment (39 - 6997, AD 91 - 11 -01) b e comes effective June 24, 1991. Issued in Renton, Washington, on May 7, 1991. Darrell M. Pederson, Acting Manager, Transport Airplane Directorate , Aircraft Certification Service. 56 FR 22306