AD 97-09-13

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that requires a one-time inspection to detect corrosion and cracking of the upper deck floor beam at station 980, and repair, if necessary. This amendment is prompted by reports of extensive corrosion found at station 980. Analysis of the corrosion indicated that fatigue cracking of the floor beam at this area could occur and cause the beam to break. The actions specified by this AD are intended to detect and correct such corrosion and/or cracking, which could cause the floor beam to break and result in extensive damage to adjacent structure and possible rapid decompression of the airplane.

Final rule

97-09-13 BOEING: Amendment 39-10009. Docket 96-NM-52-AD. \n\n\tApplicability: Model 747-300 and -400 series airplanes having line numbers up to and including 843, and Model 747 series airplanes modified to a stretched upper deck configuration; on which an upper deck cart lift has been installed at station 980; 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 otherwise 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 detect and correct corrosion and consequent fatigue cracking of the upper deck floor beam at station 980, which could cause the floor beam to break and, consequently, result in extensive damage to adjacent structure and possible rapid decompression of the airplane, accomplish the following: \n\n\t(a)\tPerform a one-time detailed visual inspection to detect corrosion and/or fatigue cracking of the upper deck floor beam at station 980 with the cart lift threshold removed, then reinstall; in accordance with Boeing Alert Service Bulletin 747-53A2400, dated December 21, 1995, at the time specified in paragraph (a)(1), (a)(2), or (a)(3) of this AD, as applicable. \n\n\tNOTE 2: Boeing Alert Service Bulletin 747-53A2400, dated December 21, 1995, specifies that the inspection described in the alert service bulletin need not be accomplished on airplanes on which the actions described in Boeing Service Bulletin 747-53-2327 have been accomplished. However, this AD requires that, for airplanes on which the actions described in Boeing Service Bulletin 747-53-2327 have been accomplished, the initial inspection required by this AD (in accordance with Boeing Alert Service Bulletin 747-53A2400) may be accomplished within 6 years after the accomplishment of those actions specified in Boeing Service Bulletin 747-53-2327. Where there are differences between this AD and the alert service bulletin, the requirements of the AD prevail. \n\n\t\t(l)\tFor airplanes that, as of the effective date of this AD, have accumulated less than 6 years since date of delivery of the airplane, or since installation of a stretched upper deck (SUD), or since the accomplishment of Boeing Service Bulletin 747-53-2327: Accomplish the inspection at the later of the times specified in paragraphs (a)(1)(i) and (a)(1)(ii) of this AD.\n \n\t\t\t(i)Within 6 years since date of delivery of the airplane, or since installation of a SUD, or within 6 years since the accomplishment of Boeing Service Bulletin 747-53-2327; whichever occurs later. Or \n\n\t\t\t(ii)\tWithin 1,500 flight cycles after the effective date of this AD. \n\t\t(2)\tFor airplanes that, as of the effective date of this AD, have accumulated 6 or more years, but less than 10 years, since date of delivery of the airplane or since installation of a SUD: Accomplish the inspection within 1,500 flight cycles or 18 months after the effective date of this AD, whichever occurs first. \n\n\t\t(3)\tFor airplanes that, as of the effective date of this AD, have accumulated 10 or more years of service since the time of initial delivery, or since the time of installation of the SUD: Except as provided by paragraph (c) of this AD, accomplish the inspection within 9 months or within 750 flight cycles after the effective date of this AD, whichever occurs first. \n\n\t(b)\tIf any corrosion or cracking is detected during the inspection required by paragraph (a) of this AD: Prior to further flight, repair the corrosion and/or cracking, and apply sealant between the threshold and the upper deck floor beam at station 980, in accordance with Boeing Alert Service Bulletin 747-53A2400, dated December 21, 1995. \n\n\t(c)\tFor airplanes that, as of the effective date of this AD, have accumulated 10 or more years of service since the time of initial delivery, or 10 or more years of service since the installation of a SUD: In lieu of accomplishing the requirements of paragraph (a) of this AD, within 9 months after the effective date of this AD, perform a one-time detailed visual inspection to detect corrosion of the upper deck floor beam at station 980 with the cart lift threshold installed, in accordance with Boeing Alert Service Bulletin 747-53A2400, dated December 21, 1995. \n\n\t\t(1)\tIf no corrosion or cracking is detected: Within 18 months or 1,500 flight cycles after the effectivedate of this AD, whichever occurs first, remove the cart lift threshold, perform a visual inspection to detect any corrosion or cracking of the upper deck floor beam at station 980, and reinstall; in accordance with the alert service bulletin. If any corrosion or cracking is detected, prior to further flight, repair the corrosion and/or cracking, and apply sealant between the threshold and the upper deck floor beam at station 980; in accordance with the alert service bulletin. \n\n\t\t(2)\tIf any corrosion or cracking is detected: Prior to further flight, remove the cart lift threshold and perform a detailed visual inspection to detect any corrosion or cracking of the upper deck floor beam at station 980; repair any corrosion and/or cracking detected; and apply sealant between the threshold and the upper deck floor beam at station 980; in accordance with the alert service bulletin. \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 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(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 747-53A2400, dated December 21, 1995. 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 effective on June 6, 1997.

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 series airplanes was published in the Federal Register on November 18, 1996 (61 FR 58667). That action proposed to require a one-time detailed visual inspection to detect corrosion and/or fatigue cracking of the upper deck floor beam at station 980 with the cart lift threshold removed, and repair, if necessary. That action also proposed to provide an alternative inspection method for older airplanes, which includes a detailed visual inspection to detect corrosion and/or fatigue cracking of the upper deck floor beam at station 980 with the cart lift threshold installed, followed later by an inspection with the cart lift threshold removed, and repair, if necessary. \n\n\tInterested persons have been afforded an opportunity to participate in the making of this amendment. Due considerationhas been given to the comments received. \n\nSupport for the Proposal \n\n\tFour commenters support the proposal.\n \nRequest to Revise the Initial Compliance Time for Certain Airplanes \n\n\tOne commenter requests that the initial inspection threshold be revised for airplanes that have been modified in accordance with Boeing Service Bulletin 747-53-2327. The commenter requests that the compliance time be changed from the proposed "within 6 years after the effective date of the AD" to "within 6 years after the accomplishment of the actions described in Boeing Service Bulletin 747-53-2327." The commenter notes that the actions described in that service bulletin include a modification to install a new increased thickness shear plate at the stairway cutout and cart lift cutout. The commenter asserts that the modification reduces the stress levels by approximately 25%, and increases the tolerance to corrosion damage. In addition, the commenter notes that Boeing Service Bulletin 747-53-2327 also includes a description of procedures to perform a detailed visual inspection for corrosion and treatment of the affected area with corrosion preventative compound BMS 3-23.\n\n\tThe FAA concurs with the commenter's request to revise the proposed compliance time. The FAA has determined that existing corrosion would be detected and corrected in accordance with Boeing Service Bulletin 747-53-2327. The FAA also acknowledges that the installation of an increased thickness shear plate will reduce the stress level of the floor beam upper chord; however, corrosion of the upper chord of the station 980 upper deck floor beam is primarily dependent on environmental conditions and time-in-service, not the stress level. Nevertheless, since the existing corrosion would be detected and corrected in accordance with that service bulletin, paragraph (a) of the final rule has been revised to specify that the initial inspection requirement of this AD may be accomplished within 6 years after theaccomplishment of the actions specified in Boeing Service Bulletin 747-53-2327. \n\nRequest to Consider Previously Accomplished Service Information \n\n\tTwo commenters request that the FAA consider accomplishment of Boeing Service Bulletin 747-53-2327, Revision 1, (which includes the application of faying surface sealant between the threshold and the floor beam chord) as an alternative method of compliance for the requirements of the proposed AD. The commenters did not explain why accomplishment of Revision 1 should be considered as an alternative method of compliance. \n\n\tThe FAA does not concur. The FAA finds that the procedures described in Boeing Service Bulletin 747-53-2327, Revision 1, do not provide adequate instructions for applying faying surface sealant between the cart lift threshold and floor beam during the modification. In light of this, the FAA has determined that there is no assurance that operators will install the faying surface sealant during the modification. However, under the provisions of paragraph (c) of the final rule, the FAA may approve requests for an alternative method of compliance if sufficient justification is presented to the FAA. \n\nRequest to Exclude Certain Airplanes from the Requirements of the AD\n\n\tOne commenter, the airplane manufacturer, requests that four Model 747-400 series airplanes that were modified to include a cart lift system in accordance with Boeing Service Bulletin 747-25-3108, be excluded from the applicability of this AD. The manufacturer states that the subject modification provides adequate instructions for the installation of faying surface sealant between the cart lift threshold and the existing station 980 floor beam.\n \n\tThe FAA acknowledges that the modification described in Boeing Service Bulletin 747-25-3108 provides adequate instructions for the installation of faying surface sealant between the cart lift threshold and the existing station 980 floor beam. However, the four airplanes listed inthe effectivity listing of that service bulletin range between line positions 891 and 927. The FAA points out that the applicability for this AD expressly states "for Model 747-300 and -400 series airplanes having line numbers up to and including 843." Therefore, no change to the final rule is necessary.\n\n Clarification of the Reinstallation Requirements of the AD: \n\n\tIn paragraph (a) of this AD, to clarify the FAA's intent that, after the one-time detailed visual inspection and any necessary repair, the cart lift threshold should be reinstalled in accordance with the alert service bulletin, the FAA has added the words "then reinstall." To further clarify this intent, in paragraph (c)(1) of this AD, the FAA has added the words "and reinstall; in accordance with the alert service bulletin." \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 therule 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 195 Model 747 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 28 airplanes of U.S. registry will be affected by this AD, that it will take approximately 19 work hours per airplane to accomplish the required actions, and that the average labor rate is $60 per work hour. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $31,920, or $1,140 per airplane. \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 onthe 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: