AD 99-17-02

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 777 series airplanes, that requires repetitive inspections of the safety spring wear plate doublers attached to the auxiliary power unit (APU) firewall, measurement of wear of the doublers, and follow-on actions, if necessary. For certain airplanes, this amendment also requires a one-time inspection to detect improper clearance between the safety spring wear plate doubler and the APU firewall, and corrective action, if necessary. This amendment also provides for optional terminating action for the repetitive inspections. This amendment is prompted by reports indicating that excessive wear was found on the safety spring wear plate doublers on the APU firewall of Boeing Model 777 series airplanes. The actions specified by this AD are intended to detect and correct wear of the safety spring wear plate doublers on the APU firewall, which could result in a hole in the APU firewall, and consequent decreased fire protection capability.

Final rule

99-17-02 BOEING: Amendment 39-11251. Docket 98-NM-275-AD. \n\n\tApplicability: Model 777 series airplanes listed as Groups 1 and 2 airplanes in Boeing Service Bulletin 777-53A0018, Revision 1, dated February 11, 1999; 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 (h) 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 wear of the safety spring wear plate doublers on the auxiliary power unit (APU) firewall, which could result in a hole in the APU firewall, and consequent decreased fire protection capability, accomplish the following: \n\nInitial Inspection \n\n\t(a)\tPerform a visual inspection of the two safety spring wear plate doublers on the APU firewall, and measure any wear of the doublers, in accordance with Boeing Service Bulletin 777-53A0018, Revision 1, dated February 11, 1999, at the time specified in paragraph (a)(1), (a)(2), or (a)(3) of this AD, as applicable. \n\n\t\t(1)\tFor airplanes that have accumulated 6,000 total flight hours or less as of the effective date of this AD: Inspect and measure prior to the accumulation of 6,300 total flight hours.\n \n\t\t(2)\tFor airplanes that have accumulated more than 6,000 but less than 10,000 total flight hours as of the effective date of this AD: Inspect and measure within 30 days after the effective date of this AD. \n\n\t\t(3)\tFor airplanes that have accumulated 10,000 total flight hours or more as of the effective date of this AD: Inspect and measure within 10 days after the effective date of this AD. \n\n\tNOTE 2: Inspections, repairs, and modifications accomplished prior to the effective date of this AD in accordance with Boeing Alert Service Bulletin 777-53A0018, dated June 29, 1998, are considered acceptable for compliance with this AD, provided that the actions required by paragraph (f) of this AD, as applicable, are accomplished in accordance with Boeing Service Bulletin 777-53A0018, Revision 1, dated February 11, 1999. \n\nRepetitive Inspections \n\n\t(b)\tIf, during the inspection required by paragraph (a) of this AD, the wear on each doubler measures less than 0.045 inch, repeat the inspection and measurement required by paragraph (a) of this AD thereafter at intervals not to exceed 60 days, in accordance with Boeing Service Bulletin777-53A0018, Revision 1, dated February 11, 1999; until paragraph (g) of this AD has been accomplished. \n\n\t(c)\tIf, during the inspection required by paragraph (a) of this AD, the wear on either doubler measures greater than or equal to 0.045 inch, but does not penetrate into or through the APU firewall: Repeat the inspection and measurement required by paragraph (a) of this AD thereafter at intervals not to exceed 30 days, in accordance with Boeing Service Bulletin 777-53A0018, Revision 1, dated February 11, 1999; until paragraph (g) of this AD has been accomplished. \n\nCorrective Actions \n\n\t(d)\tIf, during the inspection required by paragraph (a) of this AD, any wear penetrates through either doubler and into or through the APU firewall: Within 20 days after detection of the wear, accomplish either paragraph (d)(1) or (d)(2) of this AD in accordance with Boeing Service Bulletin 777-53A0018, Revision 1, dated February 11, 1999. \n\n\t\t(1)\tInstall a temporary stainless steel patchon both doublers, and within 4,000 flight cycles after installation of the temporary patch, accomplish the requirements of paragraph (e) of this AD. \n\n\t\t(2)\tAccomplish the requirements of paragraph (e) of this AD. \n\t(e)\tFor airplanes on which wear is detected that penetrates through either doubler and into or through the APU firewall: Accomplish the requirements of paragraphs (e)(1) and (e)(2) of this AD at the time specified in paragraph (d) of this AD, as applicable. \n\n\t\t(1)\tRepair the damage to the APU firewall in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. \n\n\t\t(2)\tReplace both existing wear plate doublers of the APU firewall with new stainless steel wear plate doublers in accordance with Boeing Service Bulletin 777-53A0018, Revision 1, dated February 11, 1999. Such replacement constitutes terminating action for the repetitive inspection requirements of paragraphs (b) and (c) of this AD.\n \nOne-Time Inspection \n\n\t(f)\tFor airplanes having L/N 001 through 037 inclusive that have been modified prior to the effective date of this AD in accordance with Boeing Alert Service Bulletin 777-53A0018, dated June 29, 1998: Within 4 years after the effective date of this AD, perform a one-time visual inspection to detect improper clearance between the safety spring wear plate doublers and the APU firewall, in accordance with Boeing Service Bulletin 777-53A0018, Revision 1, dated February 11, 1999. \n\n\t\t(1)\tIf the doublers are not in contact with the chemically milled pocket of the APU firewall, no further action is required by this paragraph. \n\n\t\t(2)\tIf the doublers are in contact with the chemically milled pocket of the APU firewall, prior to further flight, install shims between the safety spring wear plate doublers and the APU firewall, in accordance with Part 6 of the Accomplishment Instructions of the service bulletin. \n\nOptional Terminating Action \n\n\t(g)\tReplacement of the existing wear plate doublers of the APU firewall with new stainless steel wear plate doublers, in accordance with Boeing Service Bulletin 777-53A0018, Revision 1, dated February 11, 1999, constitutes terminating action for the repetitive inspection requirements of paragraphs (b) and (c) of this AD. \n\nAlternative Methods of Compliance \n\n\t(h)\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\nSpecial Flight Permits \n\n\t(i)\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(j)\tExcept as provided by paragraph (e)(1) of this AD, the actions shall be done in accordance with Boeing Service Bulletin 777-53A0018, Revision 1, dated February 11, 1999. 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(k)\tThis amendment becomes effective on September 17, 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 777 series airplanes was published as a supplemental notice of proposed rulemaking (NPRM) in the Federal Register on April 8, 1999 (64 FR 17130). That action proposed to require repetitive inspections of the safety spring wear plate doublers attached to the auxiliary power unit (APU) firewall, measurement of wear of the doublers, and follow-on actions, if necessary. For certain airplanes, that action also proposed to require a one-time inspection to detect improper clearance between the safety spring wear plate doubler and the APU firewall, and corrective action, if necessary. That action also provided for optional terminating action for the repetitive inspections. \n\nComments Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. \nSupport for the Proposal \n\n\tOne commenter supports the proposed rule. \n\nRequest for Extension of the Compliance Time \n\n\tOne commenter requests that the compliance time for the actions specified by paragraphs (a), (b), and (c) of the proposed AD be extended. The commenter states that it operates 34 airplanes affected by the proposed rule, including airplanes that have accumulated as many as 15,000 total flight hours. The commenter states that it has begun accomplishing the terminating action, and thus far, none of the removed wear plates show wear levels approaching penetration. Although the commenter supports the decision to mandate Boeing Alert Service Bulletin 777-53A0018, Revision 1, dated February 11, 1999, it feels that the inspection compliance times specified in paragraphs (a), (b), and (c) of the proposal are unnecessarily conservative. \n\n\tThe FAA does not concur with the commenter's request to extend the compliance time. In developing an appropriate compliance time for this action, the FAA considered the safety implications, parts availability, and normal maintenance schedules for timely accomplishment of the modification. In consideration of these items, as well as the variability in the reported wear rate of the safety spring wear plate doublers attached to the APU firewall, the FAA has determined that the compliance times specified in paragraphs (a), (b), and (c) of the AD will not place an undue hardship on the majority of affected operators, and an acceptable level of safety can be maintained. No change to the final rule is necessary. \n\nExplanation of Changes Made to the Applicability \n\n\tThe final rule has been revised to correct the applicability of the AD. In the preamble to the supplemental NPRM, the FAA discussed the difference between the effectivity listing of the alert service bulletin and the applicability of the AD. The supplemental NPRM stated that Model 777 series airplanes after line number 156 have stainless steel wear plate doublers installed prior to delivery. Since the issuance of the supplemental NPRM, the FAA has determined that there are four airplanes having line numbers less than 157 (line numbers 94, 102, 104, and 120) that had the stainless steel wear plate doublers installed prior to delivery. The alert service bulletin identifies airplanes having line numbers 94, 102, 104, 120, and 157 through 183 inclusive, as Group 3 airplanes. None of these airplanes would be subject to the unsafe condition described above; therefore, the applicability of the final rule has been revised to include only Groups 1 and 2 airplanes, as listed in the alert service bulletin. The four affected airplanes were not included in the cost impact in the proposed rule; therefore, no change is required to the cost impact.\n\nConclusion \n\n\tAfter careful review of the available data, including the comments noted above, the FAA has determined that air safety and thepublic 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\nCost Impact \n\n\tThere are approximately 152 airplanes of the affected design in the worldwide fleet. The FAA estimates that 35 airplanes of U.S. registry will be affected by this AD. \n\n\tIt will take approximately 2 work hours per airplane to accomplish the required inspection to detect wear of the safety spring wear plate doublers, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of this inspection required by this AD on U.S. operators is estimated to be $4,200, 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 proposed requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. \n\n\tShould an operator be required to accomplish the temporary repair, it will take approximately 2 work hours per airplane to accomplish the repair, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the temporary repair is estimated to be $120 per airplane. \n\n\tShould an operator be required to accomplish the inspection to detect improper clearance between the safety spring wear plate doubler and the APU firewall, it will take approximately 1 work hour per airplane to accomplish the inspection, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of this inspection is estimated to be $60 per airplane. \n\n\tShould an operator be required or elect to accomplish the replacement of the wear plate doublers, it will take approximately 3 work hours per airplane to accomplish the replacement, at an average labor rate of $60 per work hour. Required parts, if acquired from the manufacturer, will cost approximately $193 per airplane. Based on these figures, the cost impact of replacement of the wear plate doublers is estimated to be $373 per airplane. \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 smallentities 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\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: