AD 99-04-23

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 737 series airplanes, that requires repetitive ultrasonic inspections to detect broken bolts that attach the terminal support fittings to the upper part of the Body Station 1088 bulkhead, and corrective actions, if necessary. This amendment also requires eventual replacement of the existing bolts with new, improved bolts, which, when accomplished, terminates the repetitive inspection requirements of this AD. This amendment is prompted by reports that bolts that attach the terminal support fittings to the upper part of the bulkhead were found broken. The actions specified by this AD are intended to prevent such broken bolts, which could result in reduced structural integrity of the vertical fin installation and possible loss of the vertical fin.

Final rule.

99-04-23 BOEING: Amendment 39-11048. Docket 98-NM-148-AD. \n\n\tApplicability: Model 737-100, -200, and -300 series airplanes, line numbers 1 through 1485 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 (c) 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 accomplishedpreviously. \n\n\tTo prevent broken bolts that attach the terminal support fittings to the upper part of the Body Station (BS) 1088 bulkhead, which could result in reduced structural integrity of the vertical fin installation and possible loss of the vertical fin, accomplish the following: \n\n\t(a)\tWithin 18 months after the effective date of this AD, perform an ultrasonic inspection to detect broken bolts that attach the terminal support fittings to the upper part of the BS 1088 bulkhead, in accordance with Boeing Service Bulletin 737-53-1107, Revision 3, dated August 26, 1993; as revised by Notice of Status Change 737-53-1107 NSC 3, dated June 9, 1994, and Notice of Status Change 737-53-1107 NSC 4, dated September 22, 1994; or Boeing Service Bulletin 737-53-1107, Revision 4, dated February 8, 1996. \n\n\t\t(1)\tIf no broken bolt is found, repeat the ultrasonic inspection thereafter at intervals not to exceed 18 months. \n\n\t\t(2)\tIf any broken bolt is found, prior to further flight, perform the actions specified in paragraph (b) of this AD. \n\n\t(b)\tPrior to the accumulation of 20 years since date of manufacture of the airplane, or within 18 months after the effective date of this AD, whichever occurs later, remove all 16 H-11 steel alloy bolts that attach the terminal support fittings to the upper part of the bulkhead, and perform an eddy current inspection to detect cracking or corrosion of the bolt holes, in accordance with Figure 2 of Boeing Service Bulletin 737-53-1107, Revision 3, dated August 26, 1993; as revised by Notice of Status Change 737-53-1107 NSC 3, dated June 9, 1994, and Notice of Status Change 737-53-1107 NSC 4, dated September 22, 1994; or Boeing Service Bulletin 737-53-1107, Revision 4, dated February 8, 1996. \n\n\t\t(1)\tIf no cracking or corrosion is found, prior to further flight, oversize all 16 bolt holes and install new Inconel bolts, in accordance with Figure 2 of the service bulletin. Accomplishment of this installation constitutes terminating action for the repetitive inspection requirements of this AD. \n\n\t\t(2)\tIf any corrosion is found, prior to further flight, oversize the bolt hole within the limits specified in Figure 2, Step 4, of the service bulletin, and install a new Inconel bolt, in accordance with Figure 2 of the service bulletin. Accomplishment of the installation for all 16 bolt holes constitutes terminating action for the repetitive inspection requirements of this AD. If corrosion does not clean up within the limits specified in Figure 2, Step 4, of the service bulletin, prior to further flight, repair in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. \n\n\t\t(3)\tIf any cracking is found, prior to further flight, oversize the bolt hole within the limits specified in Figure 2, Step 5, of the service bulletin, and perform another eddy current inspection to ensure cracks have been removed, in accordance with Figure 2 of the service bulletin. \n\n\t\t\t(i)\tIf, after oversizing, no cracking is found, prior to further flight, oversize the bolt hole again, and install a new Inconel bolt, in accordance with Figure 2 of the service bulletin. Accomplishment of the installation for all 16 bolt holes constitutes terminating action for the repetitive inspection requirements of this AD. \n\n\t\t\t(ii)\tIf, after oversizing, any cracking is found, prior to further flight, repair in accordance with a method approved by the Manager, Seattle ACO. \n\n\tNOTE 2: Replacement of all H-11 steel alloy bolts accomplished prior to the effective date of this AD, in accordance with Boeing Service Bulletin 737-53-1107, dated October 15, 1987; Revision 1, dated June 22, 1989; or Revision 2, dated September 10, 1992; is considered acceptable for compliance with the applicable actions specified in paragraph (b) of this AD. \n\n\t(c)\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 ACO. 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 3: 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(d)\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(e)\tExcept as provided by paragraphs (b)(2) and (b)(3)(ii) of this AD, the actions shall be done in accordance with Boeing Service Bulletin 737-53-1107, Revision 3, dated August 26, 1993; as revised by Notice of Status Change 737-53-1107 NSC 3, dated June 9, 1994, and Notice of Status Change 737-53-1107 NSC 4, dated September 22, 1994; or Boeing Service Bulletin737-53-1107, Revision 4, dated February 8, 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(f)\tThis amendment becomes effective on March 29, 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 series airplanes was published in the Federal Register on July 15, 1998 (63 FR 38116). That action proposed to require repetitive ultrasonic inspections to detect broken bolts that attach the terminal support fittings to the upper part of the Body Station 1088 bulkhead, and corrective actions, if necessary. That action also proposed to require eventual replacement of the existing bolts with new, improved bolts, which, when accomplished, would terminate the requirements of the AD. \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\n\tSeveral commenters support the proposed rule. \n\nRequest to Revise Applicability of the AD \n\n\tOne commenter requeststhat the applicability of the proposed AD be revised to list the affected airplanes by specific model number. The commenter states that the proposed applicability could cause undue confusion because the next generation (737-600/-700/-800) series airplanes will start over with line number 001, and the proposal does not apply to these next generation airplanes. \n\n\tThe FAA concurs with the commenter's request. The FAA has verified that the cumulative line numbering of the next generation airplanes (737-600/-700/-800) will be reset to begin with line number 001. Additionally, the Model 737-400 and -500 series airplanes begin with line number 1486 and have a design change implemented that specifies installation of the Inconel bolts; therefore, those airplanes are not subject to the identified unsafe condition. The applicability section of the final rule has been revised to specify Model 737-100, -200 and -300 series airplanes only, line numbers 1 through 1485.\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 this change will neither increase the economic burden on any operator nor increase the scope of the AD. \n\nCost Impact \n\n\tThere are approximately 1,485 airplanes of the affected design in the worldwide fleet. The FAA estimates that 630 airplanes of U.S. registry will be affected by this AD. \tIt will take approximately 3 work hours 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 $113,400, or $180 per airplane, per inspection cycle. \n\n\tIt will take approximately 9 work hours per airplane to accomplish the required replacement, at an average labor rate of $60 per work hour. Requiredparts will cost approximately $471 per airplane. Based on these figures, the cost impact of the replacement required by this AD on U.S. operators is estimated to be $636,930, or $1,011 per 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\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: