AD 98-26-13 SUPERSEDED

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that requires a one-time inspection to determine the material type of the stop support fittings of the main entry doors. This AD also requires repetitive visual inspections to detect cracks of certain stop support fittings of the main entry doors, and replacement of any cracked stop support fitting with a certain new stop support fitting. This amendment is prompted by reports that stress corrosion cracking was found on certain stop support fittings of the main entry doors. The actions specified by this AD are intended to detect and correct such stress corrosion cracking, which could lead to failure of the stop support fittings. Failure of the stop support fittings could result in loss of a main entry door and consequent rapid decompression of the airplane.

Final rule.

98-26-13 BOEING: Amendment 39-10954. Docket 97-NM-59-AD.\n\n\tApplicability: Model 747-100, -100B, -200, -200B, -200C, -300, -400, and 747SR series airplanes; having line numbers 1 through 830 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 detect and correct stress corrosion cracking of the stop support fittings of the main entry doors and the resultant failure of the stop support fittings, which could result in loss of a main entry door and consequent rapid decompression of the airplane, accomplish the following: \n\n\t(a)\tWithin 18 months after the effective date of this AD, perform a high frequency eddy current inspection to determine the material type of the stop support fittings of the main entry doors, in accordance with the Accomplishment Instructions of Boeing Service Bulletin 747-53-2358, dated August 26, 1993. Perform the inspection only at those locations where the material type of the stop support fittings is unknown, as specified in Figure 3, Table 1, of the service bulletin. \n\n\t\t(1)\tIf the fitting is made from 7075-T73 material, no further action is required by this AD for that fitting. \n\n\t\t(2)\tIf the fitting is NOT made from 7075-T73 material,prior to further flight, perform a visual inspection to detect cracks of the stop support fitting of the main entry doors, in accordance with the service bulletin. \n\n\t\t\t(i)\tIf no crack is detected, repeat the visual inspection thereafter at intervals not to exceed 36 months or 2,000 flight cycles, whichever occurs first. \n\n\t\t\t(ii)\tIf any crack is detected, prior to further flight, replace the fitting with a stop support fitting made from 7075-T73 material, in accordance with the service bulletin. \n\n\t(b)\tReplacement of the stop support fitting of the main entry doors with a stop support fitting made from 7075-T73 material, in accordance with Boeing Service Bulletin 747-53-2358, dated August 26, 1993, constitutes terminating action for the repetitive inspection requirements of this AD for the replaced fitting. \n\n\t(c)\tAs of the effective date of this AD, no person shall install a stop support fitting made from either 7079-T651 or 7075-T651 material on any airplane. \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 Service Bulletin 747-53-2358, dated August 26, 1993. 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 January 25, 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 747 series airplanes was published in the Federal Register on March 20, 1998 (63 FR 13566). That action proposed to require a one-time inspection to determine the material type of the stop support fittings of the main entry doors. That action also proposed to require repetitive visual inspections to detect cracks of certain stop support fittings of the main entry doors, and replacement of any cracked stop support fitting with a certain new stop support fitting. \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\nSupport for the Proposal \n\n\tSeveral commenters support the proposed rule.\n\n Request to Include a Threshold for Initial Inspection \n\n\tTwo commenters request that the proposed compliance time for the initial high frequency eddy current (HFEC) inspection to determine the material type of the stop support fittings of the main entry doors be revised from 18 months after the effective date of this AD, as stated in the proposal, to 6 years after delivery of the airplane or 18 months after the effective date of the AD, whichever occurs later. One of the commenters points out that cracking of the fittings has been attributed to stress corrosion and that, when corrosion prevention is performed properly (i.e., in accordance with the Corrosion Prevention and Control Program (CPCP)), the growth of corrosion cracking is very slow. The commenter notes that corrosion and stress corrosion cracking is unlikely to occur on younger airplanes. \n\n\tThe FAA does not concur with the commenters' request to include a threshold for the initial inspection. As stated previously in the notice of proposed rulemaking (NPRM), the FAA has determined that all affected airplanes are older than 6 years since the date of manufacture of the airplane. The youngest airplane has been in service for more than seven years. Therefore, all operators are required to perform the initial inspection of the affected airplanes within 18 months after the effective date of this AD. No change to the final rule is necessary in this regard. \n\nRequest to Limit the Area of Inspection \n\n\tOne commenter requests that the proposed HFEC inspection to determine the material type of the stop support fittings of the main entry doors should be required only if the material of the stop support fittings is unknown, as specified in Figure 3, Table 1, of the referenced service bulletin. \n\n\tThe FAA concurs with the commenter that the HFEC inspection required by this AD should be required only for those stop support fittings. The FAA's intent is that the HFEC inspection be accomplished only at the locations specified in the referenced service bulletin, where the material type is unknown. The visual inspection must be accomplished only on those stop support fittings of the main entry doors that are made from either 7079-T651 or 7075-T651 material. The FAA has revised paragraph (a) of the final rule to clarify this point. \n\nRequest to Extend Repetitive Inspection Intervals \n\n\tSeveral commenters request that the repetitive interval for accomplishment of the visual inspections to detect cracks of certain stop support fittings of the main entry doors be extended from the proposed 18 months to 36 months, as specified in Boeing Service Bulletin 747-53-2358, dated August 26, 1993 (which was referenced as the appropriate source of service information in the NPRM). One of the commenters notes that the cracks on the affected stop support fittings are attributed to stress corrosion, which is a function of environment and time. As such, the inspection interval specified in the service bulletin is based on results of inspections of the fleet of Model 747 series airplanes, and on the degree of corrosion or cracking found during those inspections. Another commenter notes that the growth rate of stress corrosion cracks depends mainly on the environment and the age of the airplane, and that growth of such cracks is relatively slow when corrosion prevention measures are accomplished properly in accordance with the CPCP. \n\n\tOne of these commenters also requests that the repetitive interval for the visual inspections be extended from the proposed 18 months to 2,000 flight cycles or 36 months, whichever occurs first. That commenter points out that the 18-month intervals specified in the proposal are not consistent with the inspection intervals of 2,000 flight cycles that are specified for inspections of similar fittings at main entry door 5 that are required by AD 92-02-01, amendment 39-8137 (57 FR 5373, February 14, 1992). \n\n\tThe FAA concurs with the commenters' requests to extend the repetitive visual inspection intervals. As a result of these comments, the FAA has reviewed results from inspections of similar fittings of main entry door 5 that were accomplished in accordance with AD 92-02-01. Based on this review, the FAA has determined that repetitive inspections of fittings that are accomplished at 2,000-flight-cycle intervals are sufficient to detect cracked fittings in a timely manner. Therefore, the FAA has revised paragraph (a)(2)(i) of the final rule to state, ". . . repeat the visual inspection thereafter at intervals not to exceed 36 months or 2,000 flight cycles, whichever occurs first."\n\n Request to Allow Continued Use of Subject Stop Support Fittings \n\n\tOne commenter requests that the proposal be revised to allow cracked stop support fittings of the main entry doors to be replaced with new stop support fittings that are made from either 7079-T651 or 7075-T651 material, provided that repetitive inspections of the replacement parts are performed at intervals of 36 months. The commenter states that a non-crackedstop support fitting made from 7079-T651 or 7075-T651 material provides the required strength capability. The commenter also notes that discarding all spares of stop support fittings made from 7079-T651 or 7075-T651 material is a waste of resources.\n\n\tThe FAA infers that the commenter is requesting that paragraph (a)(2)(ii) of the proposal be revised to allow installation of new parts made from either 7079-T651 or 7075-T651 material, or parts made from 7075-T73 material, and that paragraph (c) of the proposal not be included in the final rule. The FAA does not concur with the commenter's request to allow continued use of the subject stop support fittings. The FAA has determined that the cracking of the stop support fittings of the main entry doors is caused by a combination of internal residual stress resulting from the manufacturing process, clamp-up stress from the installation of the fittings, operational stress due to pressurization of the airplane, and stress corrosion. Other parts made from 7079-T651 or 7075-T651 material previously have been found to crack while in storage, due to internal residual stress. While the FAA is not requiring the replacement of uncracked stop support fittings of the main entry doors, the FAA will not promote long-term inspections of the stop support fittings by approving the installation of replacement parts that are subject to the same unsafe condition. No change to the final rule is necessary in this regard. \n\nRequest to Amend Aging Fleet Inspection and Modification Program \n\n\tOne commenter suggests that Boeing Service Bulletin 747-53-2358 be reviewed by the 747 Structures Task Group (STG) for possible inclusion in the aging aircraft inspection or modification program. \n\n\tThe FAA infers that the commenter is requesting that the FAA delay issuance of the final rule until the STG has reviewed Boeing Service Bulletin 747-53-2358 and considered including that service bulletin in Boeing Document No. D6-35999, dated March1989, "Aging Airplane Service Bulletin Structural Modification Program, Model 747." (The FAA previously issued AD 90-06-06, amendment 39-6490 (55 FR 8374, March 7, 1990), which requires incorporation of certain structural modifications in accordance with Boeing Document No. D6-35999.)\n \n\tThe FAA does not concur. The FAA has determined that rulemaking is necessary to address the unsafe condition (stress corrosion cracking on certain stop support fittings of the main entry doors, which could result in failure of the stop support fittings, loss of a main entry door, and consequent rapid decompression of the airplane). By issuing this new rule, the FAA has taken action to ensure that the stop support fittings of the main entry doors on the affected Boeing Model 747 series airplanes are inspected and replaced, if necessary, in a timely manner. This action does not preclude a review of Boeing Service Bulletin 747-53-2358 by the STG for possible inclusion in Boeing Document No. D6-35999. However, the FAA finds that to delay this action would be inappropriate in light of the identified unsafe condition. Therefore, no change to the final rule is necessary in this regard. \n\nExplanation of Additional Changes Made to This Final Rule \n\n\tIn the proposal, paragraph (a)(1) reads, "If the fitting is made from 7075-T73 material, no further action is required by this AD." Since the issuance of the NPRM, the FAA has determined that such language could be misleading to operators, because follow-on actions are required for any stop support fitting of the main entry door that is made from 7079-T651 or 7075-T651 material, regardless of whether other stop support fittings are made from 7075-T73 material. Therefore, paragraph (a)(1) of the final rule has been revised to read, "...no further action is required by this AD for that fitting." \n\nConclusion \n\n\tAfter careful review of the available data, including the comments noted above, the FAA has determined that air safety andthe public interest require the adoption of the rule with the changes described previously. 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 515 Boeing Model 747 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 164 airplanes of U.S. registry will be affected by this AD. \n\n\tIt will take approximately 1 work hour per door to accomplish the required HFEC inspection, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the HFEC inspection required by this AD on U.S. operators is estimated to be $60 per door. \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\n\tShould an operator be requiredto accomplish the required visual inspection, it will take approximately 2 work hours per door to accomplish the required actions, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the visual inspection required by this AD on U.S. operators is estimated to be $120 per door. \n\n\tShould an operator elect to accomplish the optional terminating action that is provided by this AD action, the number of hours required to accomplish it would be approximately 124 work hours per door, at an average labor rate of $60 per work hour. Required parts would cost approximately $13,000 per door. Based on these figures, the cost impact of the optional terminating action on U.S. operators is estimated to be $20,440 per door. \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 amongthe 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 Adoption of theAmendment \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: 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:

The service information referenced in this AD may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. This information may be examined at the Federal Aviation Administration (FAA), Transport Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Bob Breneman, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2776; fax (425) 227-1181.