AD 94-02-04

This amendment adopts a new airworthiness directive (AD), applicable to all Boeing Model 727 series airplanes, that requires inspections of certain fuselage frames for cracks, and modification, if necessary; inspections to detect cracks in certain frame gussets, and replacement, if necessary; and inspections at certain body stations to detect open pilot holes and to detect cracks in any open pilot hole found, and repair and modification, if necessary. This amendment is prompted by reports of cracked frames and open pilot holes. The actions specified by this AD are intended to prevent frame failures and consequent rapid decompression of the cabin.

Final rule.

94-02-04 BOEING: Amendment 39-8802. Docket 91-NM-65-AD. \n\nApplicability: All Model 727 series airplanes, certificated in any category. \n\nCompliance: Required as indicated, unless accomplished previously. \n\nTo prevent failure of fuselage frames and depressurization of the airplane, accomplish the following: \n\n(a)\tFor airplanes identified as Group 1 or 2 in Boeing Service Bulletin 727-53-0197, Revision 1, dated April 9, 1992: Prior to the accumulation of 12,000 flight cycles since manufacture, or within 3,000 flight cycles after the effective date of this AD, whichever occurs later, perform an eddy current inspection of the fastener holes and a close visual inspection of the frame flange and web to detect cracks at body stations (BS) 760.95, 783.95, 825.95, and 848.95 in accordance with Part I of the Accomplishment Instructions of the service bulletin. \n\n(1)\tIf any crack is found, prior to further flight, install the applicable repair and preventive modification in accordance with Part III of the Accomplishment Instructions of the service bulletin. Once this repair and preventive modification is installed, no further eddy current inspections of the fastener holes or close visual inspections of the modified frame flange and web are required by this AD. \n\n(2)\tIf no crack is found, prior to further flight, accomplish one of the procedures identified in paragraphs (a)(2)(i), (a)(2)(ii), or (a)(2)(iii) of this AD, in accordance with Part I, paragraph E., of the Accomplishment Instructions of the service bulletin. \n\n(i)\tOversize the hole by 1/32 inch and install an oversized fastener. Prior to the accumulation of 12,000 flight cycles after oversizing the hole, and thereafter at intervals not to exceed 6,000 flight cycles, continue to accomplish the inspections required by paragraph (a) of this AD. If any crack is found, prior to further flight, install the applicable repair and preventive modification in accordance with Part III of the Accomplishment Instructions of the service bulletin. Once this repair and preventive modification is installed, no further eddy current inspections of the fastener holes or close visual inspections of the frame flange and web are required by this AD. Or \n\n(ii)\tInstall the same size fastener that was removed. Thereafter at intervals not to exceed 6,000 flight cycles, continue to accomplish the inspections required by paragraph (a) of this AD. If cracks are found, prior to further flight, install the applicable repair and preventive modification in accordance with Part III of the Accomplishment Instructions of the service bulletin. Once this repair and preventive modification is installed, no further eddy current inspections of the fastener holes or close visual inspections of the frame flange and web are required by this AD. Or \n\n(iii)\tInstall the applicable repair and preventive modification in accordance with Part III of the Accomplishment Instructions of the service bulletin. Once this repair and preventive modification is installed, no further eddy current inspections of the fastener holes or close visual inspections of the frame flange and web are required by this AD. \n\n(b)\tFor airplanes identified as Group 3, 4, or 5 in Boeing Service Bulletin 727-53-0197, Revision 1, dated April 9, 1992: Prior to the accumulation of 12,000 flight cycles since manufacture, or within 3,000 flight cycles after the effective date of this AD, whichever occurs later, perform an eddy current inspection of the fastener holes and a close visual inspection of the frame flange and web to detect cracks at body stations (BS) 760.95 and 783.95 in accordance with Part II of the Accomplishment Instructions of the service bulletin. \n\n(1)\tIf any crack is found, prior to further flight, install the applicable repair and preventive modification in accordance with Part IV of the Accomplishment Instructions of the service bulletin. Once this repair and preventive modification is installed, no further eddy current inspections of the fastener holes or close visual inspections of the frame flange and web are required by this AD. \n\n(2)\tIf no crack is found, prior to further flight, accomplish one of the procedures identified in paragraphs (b)(2)(i), (b)(2)(ii), or (b)(2)(iii) of this AD, in accordance with Part II, paragraph E. of the Accomplishment Instructions of the service bulletin: \n\n(i)\tOversize the hole by 1/32 inch and install an oversized fastener. Prior to the accumulation of 12,000 flight cycles after oversizing the hole, and thereafter at intervals not to exceed 6,000 flight cycles, continue to accomplish the inspections required by paragraph (b) of this AD. If cracks are found, prior to further flight, install the applicable repair and preventive modification in accordance with Part IV of the Accomplishment Instructions of the service bulletin. Once this repair and preventive modification is installed, no further eddy current inspections of the fastener holes or close visual inspections of the frame flange and web are required by this AD. Or \n\n(ii)\tInstall the same size fastener that was removed. Thereafter at intervals not to exceed 6,000 flight cycles, continue to accomplish the inspections required by paragraph (b) of this AD. If cracks are found, prior to further flight, install the applicable repair and preventive modification in accordance with Part IV of the Accomplishment Instructions of the service bulletin. Once this repair and preventive modification is installed, no further eddy current inspections of the fastener holes or close visual inspections of the frame flange and web are required by this AD. Or \n\n(iii)\tInstall the applicable repair and preventive modification in accordance with Part IV of the Accomplishment Instructions of the service bulletin. Once this repair and preventive modification is installed, no further eddy current inspections of the fastener holes or close visual inspections of the frame flange and web arerequired by this AD. \n\n(c)\tFor airplanes identified as Group 1, 2, 3, or 4 in Boeing Service Bulletin 727- 53-0197, Revision 1, dated April 9, 1992: Prior to the accumulation of 12,000 flight cycles since manufacture, or within 3,000 flight cycles after the effective date of this AD, whichever occurs later, perform a close visual inspection to detect cracks in the frame gussets at BS 825.95 in accordance with Part V (for Groups 1 and 2 airplanes) or Part VI (for Groups 3 and 4 airplanes) of the Accomplishment Instructions of the service bulletin. Repeat these inspections thereafter at intervals not to exceed 6,000 flight cycles. \n\n(1)\tIf any crack is found, prior to further flight, replace the gusset with a new gusset in accordance with Figure 10 (for Groups 1 and 2 airplanes) or Figure 11 (for Groups 3 and 4 airplanes) of the service bulletin. \n\n(2)\tReplacement of the gusset in accordance with paragraph (c)(1) of this AD constitutes terminating action for the repetitive inspections required by paragraph (c) of this AD. \n\n(d)\tFor airplanes identified as Group 1, 2, 3, 4, or 5 in Boeing Service Bulletin 727- 53-0197, Revision 1, dated April 9, 1992: Prior to the accumulation of 12,000 flight cycles since manufacture, or within 3,000 flight cycles after the effective date of this AD, whichever occurs later, perform a close visual inspection of the inner flange of the frames and the strap on the inner flange at BS 760.95 and 783.95 to detect open pilot holes in accordance with Part VII of the Accomplishment Instructions of the service bulletin. \n\n(1)\tIf no open pilot hole is found, no further action is required by paragraph (d) of this AD. \n\n(2)\tIf any open pilot hole is found, perform a close visual inspection to detect cracks in that open pilot hole. A "close visual inspection" is defined as a close, intensive visual inspection of highly defined structural details or locations, searching for evidence of structural irregularity and using adequate lighting. In addition, inspection aids such as mirrors, etc., surface cleaning, and access procedures are required, as necessary, to gain proximity. \n\n(i)\tIf no crack is found in any open pilot hole, repeat the inspection required by paragraph (d)(2) of this AD thereafter at intervals not to exceed 6,000 flight cycles until the preventive modification specified in paragraph (d)(2)(ii) or (d)(2)(iii) of this AD, as applicable, is installed. \n\n(ii)\tIf any crack is found in an open pilot hole that is located inside any of the shaded areas shown in Figures 3, 4, and 5 of the service bulletin, prior to further flight, repair the crack in the pilot hole and install a preventive modification in accordance with Part III or IV of the Accomplishment Instructions of the service bulletin. Installation of a preventive modification constitutes terminating action for the repetitive inspections of the open pilot holes specified in paragraph (d)(2)(i) of this AD. \n\n(iii)\tIf any crack is found in anopen pilot hole that is located outside any of the shaded areas shown in Figures 3, 4, and 5 of the service bulletin, prior to further flight, repair the crack in the pilot hole in accordance with Part III or IV of the Accomplishment Instructions of the service bulletin, and install a preventive modification in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Installation of a preventive modification constitutes terminating action for the repetitive inspections of the open pilot holes specified in paragraph (d)(2)(i) of this AD. \n\n(e)\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, 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.NOTE: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO. \n\n(f)\tSpecial flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate the airplane to a location where the requirements of this AD can be accomplished. \n\n(g)\tThe actions shall be done in accordance with Boeing Service Bulletin 727-53-0197, Revision 1, dated April 9, 1992. 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(h)\tThis amendment becomes effective on March 3, 1994.

A proposal to amend part 39 of the Federal Aviation Regulations to include an airworthiness directive (AD) that is applicable to all Boeing Model 727 series airplanes was published as a supplemental notice of proposed rulemaking (NPRM) in the Federal Register on May 7, 1993 (58 FR 27217). That action proposed to require inspections of certain fuselage frames for cracks, and modification, if necessary; inspections to detect cracks in certain frame gussets, and replacement, if necessary; and inspections at certain body stations to detect open pilot holes and to detect cracks in any open pilot hole found, and repair and modification, if necessary. \n\nInterested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. \n\nOne commenter supports the proposed rule. \n\nOne commenter, Boeing, requests that the proposed rule be withdrawn and suggests that the service bulletin cited in the proposal be incorporated into the structural modification and inspection program for aging airplanes. Boeing references a similar situation involving the overwing stub frames on Model 737 series airplanes. No AD was issued in that instance; instead, the preventive modification was made part of the aging fleet modification program at life goal. Boeing also states that including the service bulletin cited in the proposal in the modification program would reduce the number of AD's concerning that subject. \n\nBoeing also believes that the consequence of frame failures was overstated in the proposal. Boeing indicates that although dozens of cases of basic frame cracking have occurred, only four cases of inboard strap cracking and no cases of frame outboard reinforcing strap cracking have been reported. Boeing adds that for rapid decompression to occur, the skin must crack; and there have been no reports of skin cracks in this area as a result of frame cracks. Boeingbelieves that rapid decompression is extremely unlikely because there is ample reinforcing structure in this area. \n\nThe FAA does not concur with the commenter's request to withdraw the proposal. Although there have been no reports of outboard strap or skin cracking, the FAA has determined that the potential exists for failure of the frames, which could lead to failure of the straps and skin in the absence of the repair and preventive modification or inspection program. Such failures would result in rapid decompression of the airplane. The FAA finds that it is not warranted to delay the proposed repair for inclusion in the aging airplane program. \n\nThe Air Transport Association (ATA) of America, on behalf of two of its members, requests that the FAA reconsider the proposed requirement of this AD to remove fasteners prior to inspection and, if necessary, require another inspection to verify the existence of cracks without fastener removal. One commenter suggests that an option should be included in the final rule that would allow visual inspections at more frequent intervals in lieu of the proposed fastener removal and eddy current inspections. Another commenter suggests that fastener removal should be required only during the initial inspection, and that subsequent inspections should be accomplished using visual and high frequency eddy current inspection methods. This commenter states that accomplishment of these suggested subsequent inspections will ensure that a crack does not reach a critical length. ATA expresses concern that continual removal of fasteners may initiate crack development. \n\nThe FAA does not concur with the commenters' requests to revise the intervals or procedures specified in this AD for inspections involving fastener removal. The FAA has reconsidered various alternatives to the inspection methods and intervals specified in this AD in light of available crack growth analysis data. The FAA finds that eddy current inspections with fasteners in place would be required at intervals of 1,500 flight cycles, or four times as often as the interval of 6,000 flight cycles (with fasteners removed) specified in this AD. Further, the FAA finds that if fastener removal were only required during the initial inspection and subsequent eddy current inspections with fasteners in place were required, the first inspection interval would be 6,000 flight cycles with subsequent inspection intervals of 1,500 flight cycles. In light of the safety implications and practical aspects of an orderly inspection of the fleet during regular maintenance periods, the FAA considers inspections with fasteners removed at intervals of 6,000 flight cycles to be the appropriate requirement for this AD. However, the FAA would consider a request for an adjustment of the inspection methods or intervals, in accordance with the provisions of paragraph (e) of this AD, provided that, for example, data is submitted to substantiate that such methods or intervals ensure that cracks will not reach a critical length. \n\nOne commenter requests that credit be given in paragraph (d) of the proposal for inspections to detect open pilot holes performed in accordance with the original issue of the service bulletin. The commenter asks specifically that the proposal be revised to state that repairs accomplished in accordance with the Model 727 Structural Repair Manual (SRM) are acceptable, provided repetitive inspections are performed thereafter at intervals of 6,000 flight cycles. This commenter has inspected the addressed area in accordance with the original issue of the service bulletin. The commenter indicates that the area targeted for inspection in paragraph (d) of the proposal is essentially the same area identified in the original issue of the service bulletin. The commenter is confident that any cracks in the pilot holes would have been detected during that inspection (and subsequently repaired) in accordance with that issue of the service bulletin. The commenter adds that airplanes inspected in accordance with the original issue of the service bulletin may have been repaired in accordance with chapter 51-40-3 of the SRM, as specified in that service bulletin. The commenter states that Boeing has not included a reference to the SRM repair in Revision 1 of the service bulletin because the SRM repair is not easily adapted to the subject frames. However, Revision 1 of the service bulletin indicates that repairs installed in accordance with the original issue of the service bulletin are adequate as long as repetitive inspections are accomplished. \n\nSimilarly, one commenter requests that paragraphs (b) and (c) of the proposal, which address (in part) inspections of the fastener holes, the frame flange and web, and certain frame gussets, be revised to allow credit for inspections accomplished previously in accordance with the original issue of the service bulletin in that the proposed compliance time should be longerfor airplanes that have been inspected previously in accordance with the original issue of the service bulletin than for those airplanes that have not been inspected. The commenter states that any cracks in the pilot holes would have been detected during inspections accomplished in accordance with the original issue of the service bulletin. \n\nThe FAA does not concur with the commenters' requests to allow credit for inspections accomplished in accordance with the procedures described in the original issue of the service bulletin. The original issue of the service bulletin does not contain procedures for inspections to detect cracks in open pilot holes, which is a requirement of this AD. Consequently, the FAA cannot be certain that operators that accomplished procedures specified in the original issue of the service bulletin also inspected for and repaired cracks in open pilot holes, as required by this AD. \n\nAnother commenter requests that plugging uncracked pilot holes in accordance with Part VII of the service bulletin be considered optional terminating action for the repetitive inspections proposed in paragraph (d)(2)(i) of this AD. The FAA does not concur. The location of pilot holes in the members of the built-up structure has been shown to vary; therefore, since all of the open pilot holes may not be visible during an inspection, it is possible that "figure 8 holes" could exist on the inner members of that structure. These figure 8 holes are two holes that have not been drilled concentrically. The danger of figure 8 holes is that they have been shown to create very high local stress. In light of this hazard, the FAA cannot allow plugging uncracked pilot holes to be considered terminating action for the repetitive inspections discussed previously. \n\nThis commenter also requests that reference to Part VI of the Accomplishment Instructions of the service bulletin be removed from paragraph (d)(2) of the proposal. The commenter states that the procedures described in Part VI of the Accomplishment Instructions of the service bulletin are not applicable to this paragraph of the proposal. \n\nThe FAA concurs partially. The FAA's intent in referring to Part VI of the Accomplishment Instructions of the service bulletin was simply to specify that the appropriate inspection technique to be performed is a close visual inspection, which is referenced in Part VI of the Accomplishment Instructions of the service bulletin. However, the FAA recognizes that clarification of this inspection method is necessary. Therefore, paragraph (d)(2) of this final rule has been revised by removing reference to Part VI of the Accomplishment Instructions of the service bulletin and by specifying that a "close visual inspection" is defined as a close intensive visual inspection of highly defined structural details or locations, searching for evidence of structural irregularity and using adequate lighting. In addition, inspection aids such as mirrors, etc.,surface cleaning, and access procedures are required, as necessary, to gain proximity. \n\nThe commenter also requests that paragraph (d)(2)(iii) be revised to delete the phrase, "in accordance with ... the service bulletin." The commenter states that repair of any crack found in an open pilot hole that is located outside any of the shaded areas shown in Figures 3, 4, and 5 of the service bulletin cannot be separated from the preventive modification. \n\nThe FAA does not concur. Repair of a crack in an open pilot hole and installation of the preventive modification are two different items. While the service bulletin contains instructions for repairing cracks, it does not specify how to install the modification if the cracked pilot hole is located outside the shaded area covered by the service bulletin. Consequently, operators are required to request approval from the FAA of a method of installating the modification. \n\nThe final rule has been revised to correct certain typographical errors in regard to paragraph and service information references, as follows: \n\n1.\tParagraph (d)(1) has been revised to clarify that if no open pilot hole is found, no further action is required by paragraph (d) of this AD. \n2.\tParagraph (d)(2)(i) of this AD has been changed to refer to paragraphs (d)(2)(ii) and (d)(2)(iii), rather than paragraphs (d)(1)(ii) and (d)(1)(iii), respectively. \n3.\tParagraph (d)(2)(ii) of this AD has been revised to refer to paragraph (d)(2)(i), rather than paragraph (d)(1)(i). \n4.\tParagraph (d)(2)(iii) of this AD has been changed to refer to paragraph (d)(2)(i), rather than paragraph (d)(1)(i). \n\nAdditionally, for consistency with the service bulletin, paragraphs (a) and (b) of this AD have been revised to include the word "repair" where any reference is made to the preventive modification. This word is added to clarify the FAA's intent that when cracks are found, operators must install the applicable "repair and preventive modification." \n\nAfter 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 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\nThere are approximately 1,695 Model 727 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 1,172 airplanes of U.S. registry will be affected by this AD, that it will take approximately 53 work hours per airplane to accomplish the required actions, and that the average labor rate is $55 per work hour. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $3,416,380, or $2,915 per airplane. This total cost figure assumes that no operator has yet accomplished the requirements of this AD. \n\nThe 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\nFor 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\nAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \nAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends 14 CFR part 39 of the Federal Aviation Regulations as follows: \n\nPART 39 - AIRWORTHINESS DIRECTIVES \n1.\tThe authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89. \n\n§ 39.13 - (Amended) \n2.\tSection 39.13 is amended by adding the following new airworthiness directive: