AD 99-04-11

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 737-600, -700, and -800 series airplanes, that requires repetitive inspections to detect damage of the aft strut insulation blanket. This AD also requires eventual replacement of the insulation blankets with new, improved blankets, which constitutes terminating action for the requirements of this AD. This amendment is prompted by reports of damaged aft strut insulation blankets. The actions specified by this AD are intended to prevent such damage, which could result in exposure of the lower surface of the strut to extreme high temperatures, consequent creation of a source of fuel ignition, and increased risk of a fuel tank explosion and fire.

Final rule.

99-04-11 BOEING: Amendment 39-11035. Docket 98-NM-258-AD. \n\n\tApplicability: Model 737-600, -700, and -800 series airplanes, line numbers 1 through 64 inclusive, 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 (d) 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 prevent damage of the aft strut insulation blankets, which could result in exposure of the lower surface of the strut to extreme high temperatures, consequent creation of a source of fuel ignition, and increased risk of a fuel tank explosion and fire, accomplish the following: \n\n\t(a)\tWithin 500 flight hours since date of manufacture of the airplane, or within 30 days after the effective date of this AD, whichever occurs later, perform a visual or borescope inspection to detect damage (cracks greater than 2.00 inches and/or separation of the face sheet) of the aft strut insulation blanket, part number (P/N) S315A213-42, in accordance with Boeing Alert Service Bulletin 737-54A1038, dated May 7, 1998, as revised by Notice of Status Change 737-54A1038 NSC 01, dated June 18, 1998. Thereafter, repeat the visual or borescope inspection at intervals not to exceed 250 flight hours. \n\n\t(b)\tIf damage (cracks greater than 2.00 inches and/or separation of the face sheet) ofany aft strut insulation blanket is detected during any inspection required by paragraph (a) of this AD, prior to further flight, accomplish either paragraph (b)(1) or (b)(2) of this AD. \n\n\t\t(1)\tReplace any damaged insulation blanket having P/N S315A213-42 with a new insulation blanket having P/N S315A213-42, in accordance with Boeing Alert Service Bulletin 737-54A1038, dated May 7, 1998, as revised by Notice of Status Change 737-54A1038 NSC 01, dated June 18, 1998. Thereafter, repeat the visual or borescope inspection required by paragraph (a) of this AD at intervals not to exceed 250 flight hours. Or \n\n\t\t(2)\tReplace any damaged insulation blanket having P/N S315A213-42 with a new, improved insulation blanket having P/N S315A213-47, in accordance with Boeing Alert Service Bulletin 737-54A1038, dated May 7, 1998, as revised by Notice of Status Change 737-54A1038 NSC 01, dated June 18, 1998. Accomplishment of this replacement constitutes terminating action for the repetitive inspection requirements of this AD. \n\n\t(c)\tWithin 18 months after the effective date of this AD, replace any aft strut insulation blanket having P/N S315A213-42 with a new, improved insulation blanket having P/N S315A213-47, in accordance with Boeing Alert Service Bulletin 737-54A1038, dated May 7, 1998, as revised by Notice of Status Change 737-54A1038 NSC 01, dated June 18, 1998. Accomplishment of this replacement constitutes terminating action for the 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 2: 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 actions shall be done in accordance with Boeing Alert Service Bulletin 737-54A1038, dated May 7, 1998, as revised by Notice of Status Change 737-54A1038 NSC 01, dated June 18, 1998. 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 effectiveon March 18, 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 737-600, -700, and -800 series airplanes was published in the Federal Register on October 15, 1998 (63 FR 55343). That action proposed to require repetitive inspections to detect damage of the aft strut insulation blanket. That action also proposed to require eventual replacement of the insulation blankets with new, improved blankets, which would constitute terminating action for the requirements of the AD. \n\nComments \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 express no objection to the proposed rule, and one commenter supports the proposed rule. \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 as proposed. \n\nCost Impact \n\n\tThere are approximately 33 Model 737-600, -700, and -800 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 26 airplanes of U.S. registry will be affected by this AD. \n\n\tIt will take approximately 1 work hour per airplane to accomplish the required inspection, at an average labor rate of $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 $1,560, or $60 per airplane, per inspection cycle. \n\n\tIt will take approximately 1 work hour per airplane to accomplish the required replacement, at an average labor rate of $60 per work hour. Required parts will be provided by the manufacturer at no cost to the operators. Based on these figures, the cost impact of the replacement required by this AD on U.S. operators is estimated to be $1,560, or $60per airplane. \n\n\tThe cost impact figures discussed above are 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. \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\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: