AD 94-06-11 ACTIVE

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 737-300, -400, and -500 series airplanes, that requires modification of the leading edge slat access panel and internal structure at Front Spar Station (FSS) 250.663. This amendment is prompted by reports that fuel leaking from the fuel line at FSS 250.663 flowed through a drain hole in a slat access panel and leaked into the turbine exhaust area. The actions specified by this AD are intended to prevent drainage from such a fuel leak into the turbine exhaust area, which could cause an external fire under the wing.

Final rule

94-06-11 BOEING: Amendment 39-8858. Docket 93-NM-146-AD. \n\n\tApplicability: Model 737-300, -400, and -500 series airplanes, line position 1001 through 1976 inclusive, 1978 through 2183 inclusive, 2185 through 2186 inclusive, and 2188 through 2193 inclusive; certificated in any category. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent drainage from a fuel line leak within the wing leading edge from entering the turbine exhaust area, which could cause an external fire under the wing, accomplish the following: \n\n\t(a)\tWithin 24 months after the effective date of this AD, modify the leading edge slat access panel and internal structure at Front Spar Station (FSS) 250.663 in accordance with Boeing Service Bulletin 737-57-1221, dated August 6, 1992. \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 CertificationOffice (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 modification shall be done in accordance with Boeing Service Bulletin 737-57- 1221, dated August 6, 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(e)\tThis amendment becomes effective on April 21, 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 737-300, -400, and -500 series airplanes was published in the Federal Register on November 16, 1993 (58 FR 60415). That action proposed to require modification of the leading edge slat access panel and internal structure at Front Spar Station (FSS) 250.663. \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\tOne commenter supports the proposal. \n\n\tAnother commenter suggests that certain wording used in the preamble to the notice to describe the unsafe condition be clarified. This commenter notes that the preamble described the proposed actions as intended to "prevent such a fuel leak (from causing an external fire under the wing);" however, the actual intent of the proposed actions is to"prevent drainage from such a fuel leak into the turbine exhaust area (which could cause an external fire under the wing)." The FAA concurs with the commenter' suggestion and has revised certain wording in the preamble to this final rule accordingly. \n\n\tThis commenter also suggests that the preamble to the notice contained an inaccurate statement in the Discussion section, which indicated that ". . .The resultant fire could spread from the turbine exhaust area to the strut and, subsequently, could ignite fuel within the strut." The commenter points out that the strut drain system would route leakage clear of the exhaust area and, therefore, the strut would not contain fuel to be ignited. The commenter suggests that condition being addressed is the result of fuel leakage draining from the wing leading edge slat access panel outboard of the strut. The proposed corrective modification involves closing the slat access panel drain and rerouting the drainage from this area into the strut drain system, which will ensure that the drainage is discharged clear of the turbine exhaust area. The FAA does not concur that this statement was totally inaccurate. However, in order to provide some clarification of this issue, the FAA considers that a more precise description of the situation prompting the addressed unsafe condition is ". . .The resultant fire could spread from the turbine exhaust area to the wing leading edge slat, and subsequently spread to the wing front spar at FSS 250.663." \n\n\tThis same commenter requests that the FAA delay issuance of the rule until a revised version of the referenced service bulletin is issued in mid-April. This revised service bulletin will include procedures for an optional method of closing the drain hole in the slat access panel. The FAA does not concur that delaying issuance of this rule, for the reasons cited by the commenter, is appropriate. If a revised service bulletin is released sometime in the future, the use of it as analternative method for complying with this rule may be requested under the provisions of paragraph (b) of this final rule. \n\n\tSeveral commenters request that the proposed compliance time of 12 months be extended to 60 months, so that the modification can be accomplished during a regularly scheduled "heavy" maintenance interval when the airplane is brought to the main maintenance base for an extended hold. These commenters point out that adoption of the proposed 12-month compliance time would require affected operators to schedule special times for the accomplishment of this modification, at significant additional expense. These commenters consider that such an extension is justified since a fuel leak of the type addressed by the proposed AD is limited to ground operations after the engines have been shut down; the risk of injury to personnel under this scenario is considerably less than a potential fire threat during airborne operations. The FAA concurs that the compliance time can be extended somewhat. Upon reconsideration, the FAA finds that the proposed 12-month compliance time may impose an undue economic burden on affected operators. The FAA has determined that extending the compliance time for modification to 24 months will not compromise safety. In addition, it will allow operators to accomplish the modification during a regularly scheduled "C" check maintenance interval at a main base, where special equipment and trained maintenance personnel will be available, if required. Paragraph (a) of the final rule has been revised accordingly. \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 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\n\tThere are approximately 950 Model 737-300, -400, and -500 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 400 airplanes of U.S. registry will be affected by this AD, that it will take approximately 10 work hours per airplane to accomplish the required actions, and that the average labor rate is $55 per work hour. The cost of required parts is expected to be negligible. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $220,000, or $550 per airplane. \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 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 authoritydelegated 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. \n\n§ 39.13 - (Amended) \n\t2.\tSection 39.13 is amended by adding the following new airworthiness directive:

The service information referenced in this AD may be obtained from Boeing\nCommercial 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.

Stephen Bray, Aerospace Engineer, Propulsion Branch, ANM-140S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (206) 227-2681; fax (206) 227-1181.