AD 94-09-13 ACTIVE

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that requires replacement of certain pneumatic duct couplings with redesigned couplings. This amendment is prompted by reports of failures of certain duct couplings installed on the wing leading edge pneumatic duct. The actions specified by this AD are intended to prevent such failures, which could lead to structural damage to the wing leading edge, flight control problems, or fire.

Final rule

94-09-13 BOEING: Amendment 39-8902. Docket 93-NM-164-AD. \n\n\tApplicability: Model 747 series airplanes, line position 1 through 219 inclusive; certificated in any category. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent failure of duct couplings installed on the wing leading edge pneumatic duct installed in the vicinity of the strut, which could lead to structural damage to the wing leading edge, flight control problems, or fire, accomplish the following: \n\n\t(a)\tWithin 15 months after the effective date of this AD, replace duct couplings having part number (P/N) 7540600 and 7540602, with duct couplings having P/N 7541749 and 7541751, in accordance with Purolator Service Bulletin FSC-912, dated December 1972, at the following locations: \n\n\t\t(1)\tThe coupling that connects the tee duct at the inboard struts to the pneumatic ducting of the engine in the struts; \n\n\t\t(2)\tThe coupling that connects the tee duct at the inboard struts to the pneumatic ducting of the wing leading edge outboard of the inboard struts; and \n\n\t\t(3)\tThe coupling that connects the pneumatic ducting of the wing leading edge to the pneumatic ducting of the engine in the outboard struts. \n\n\t(b)\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\nNOTE: 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(c)\tSpecial flight permits may be issued in accordance with Federal Aviation Regulations (FAR) 21.197 and 21.199 to operate the airplane to a location where the requirements of this AD can be accomplished. \n\n\t(d)\tThe replacement shall be done in accordance with Purolator Service Bulletin FSC-912, dated December 1972. 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 PTI Technologies, Inc., 950 Rancho Conejo Boulevard, Newbury Park, California 91320. 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(e)\tThis amendment becomes effective on June 17, 1994.

A proposal to amend part 39 of the Federal Aviation Regulations to include an airworthiness directive (AD) that is applicable to certain Boeing Model 747 series airplanes was published in the Federal Register on December 9, 1993 (58 FR 64707). That action proposed to require replacement of certain pneumatic duct couplings installed on the wing leading edge pneumatic duct. \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\tTwo commenters support the proposal. \n\n\tOne commenter requests that the proposal be revised to permit operators to perform repetitive dye penetrant inspections to detect fatigue cracking of the duct couplings at intervals of 15 months, in lieu of the proposed mandatory replacement of the couplings at 15 months. This commenter states that it has found only one failure of a duct coupling, but the failed coupling was ata location different from that addressed by the proposal. Additionally, the commenter found excess misalignment of the pneumatic ducts at the location of the failed duct, and considers that this situation contributed to the coupling failure. The commenter has already performed a dye penetrant inspection of the wing leading edge pneumatic duct couplings on its fleet of affected airplanes, but has found no fatigue cracking. The FAA does not concur with the commenter's request for several reasons. First, dye penetrant inspections have not been shown to be a reliable method for detecting cracks in the couplings. Second, the couplings in the vicinity of the struts (addressed by this AD action) are of highest concern, because of the increased risk of damage in that area, should a duct burst. Third, the misalignment referred to by the commenter has been found to be associated with maintenance activity; this problem has been addressed with improved installation instructions that have been added recently to the Model 747 Maintenance Manual. While misalignment has been shown to be a contributing factor in the coupling failures, fatigue cracking is the main concern. The new design couplings that were installed on airplanes beginning at line number 220, and that are required to be installed in accordance with this AD, have not exhibited any fatigue or other failures. In light of these items, the FAA has determined that installation of the new design couplings is both appropriate and warranted. \n\n\tAnother commenter requests that the proposal be revised to include the option of performing an aided visual inspection of the subject couplings within 15 months and replacement of the couplings within 24 months. The FAA does not concur. The FAA does not consider a visual inspection to be adequate for detecting critical cracks in the couplings, even as an interim measure. The FAA has determined that replacement of the couplings with the new design couplings is the only method to effectively address the unsafe condition presented by failure of the subject couplings. \n\n\tOne commenter requests that the proposed compliance time of 15 months be extended to 18 months in order to allow the replacement to be accomplished during the time of this commenter's regularly scheduled "C" check. The commenter states that the adoption of the proposed compliance time of 15 months would require that special times be scheduled for the accomplishment of this replacement, at additional expense. The FAA does not concur. The proposed compliance time was selected based on the average "C" check interval for the majority of affected operators. It was also selected based on the degree of urgency associated with addressing the subject unsafe condition, the availability of required parts, and the practical aspect of replacing the required parts within a maximum interval of time allowable for all affected airplanes to continue to operate without compromising safety. In light ofthese items, the FAA has determined that 15 months for compliance is appropriate. However, paragraph (b) of the final rule does provide affected operators the opportunity to apply for an adjustment of the compliance time if sufficient data are presented to justify such an adjustment. \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 as proposed. \n\n\tThere are approximately 219 Model 747 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 132 airplanes of U.S. registry will be affected by this AD, that it will take approximately 12 work hours per airplane to accomplish the required actions, and that the average labor rate is $55 per work hour. Required parts will cost approximately $8,486 per airplane. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $1,207,272, or $9,146 perairplane. \n\n\tThe number of required work hours for the replacement of the duct couplings, as indicated above, is presented as if the accomplishment of that action was to be conducted as a "stand alone" action. However, the 15-month compliance time specified in paragraph (a) of this AD should allow ample time for the duct coupling replacement to be accomplished coincidentally with scheduled major airplane inspection and maintenance activities, thereby minimizing the costs associated with special airplane scheduling. \n\n\tThe total 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\tThe FAA recognizes that the obligation to maintain aircraft in an airworthy condition is vital, but sometimes expensive. Because AD's require specific actions to address specific unsafe conditions, they appear to imposecosts that would not otherwise be borne by operators. However, because of the general obligation of operators to maintain aircraft in an airworthy condition, this appearance is deceptive. Attributing those costs solely to the issuance of this AD is unrealistic because, in the interest of maintaining safe aircraft, most prudent operators would accomplish the required actions even if they were not required to do so by the AD. \n\n\tA full cost-benefit analysis has not been accomplished for this AD. As a matter of law, in order to be airworthy, an aircraft must conform to its type design and be in a condition for safe operation. The type design is approved only after the FAA makes a determination that it complies with all applicable airworthiness requirements. In adopting and maintaining those requirements, the FAA has already made the determination that they establish a level of safety that is cost- beneficial. When the FAA, as in this AD, makes a finding of an unsafe condition, this means that this cost-beneficial level of safety is no longer being achieved and that the required actions are necessary to restore that level of safety. Because this level of safety has already been determined to be cost-beneficial, a full cost-benefit analysis for this AD would be redundant and unnecessary. \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\nAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\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 \n\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. § 39.13 - (Amended) \n\n2.\tSection 39.13 is amended by adding the following new airworthiness directive:

The service information referenced in this AD may be obtained from PTI\nTechnologies, Inc., 950 Rancho Conejo Boulevard, Newbury Park, California 91320. This\ninformation may be examined at the Federal Aviation Administration (FAA), Transport Airplane\nDirectorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the\nFederal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Barbara Mudrovich, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (206) 227-2670; fax (206) 227-1181.