AD 93-17-02

93-17-02 BOEING: Amendment 39-8672. Docket 93-NM-05-AD. Supersedes AD 91-20-11, Amendment 39-8045.

Applicability: Model 737-300, -400, and -500 series airplanes, line positions through 2428, inclusive; and Model 737-200 series airplanes, equipped with DC powered fuel tank float switches; certificated in any category.

Compliance: Required as indicated, unless accomplished previously.

To prevent failure of the wing main tank float switch electrical conduits and subsequent fuel leakage resulting in an engine tail pipe fire, accomplish the following:

(a) For airplanes listed in Boeing Service Letter 737-SL-28-36, dated November 30, 1990: Within 90 days after November 7, 1991 (the effective date of AD 91-20-11, Amendment 39-8045), and thereafter at intervals not to exceed 1,500 flight hours, perform an inspection of the wing main tank float switch electrical conduits for fuel leakage and condensation build-up, in accordance with Boeing Service Letter 737-SL-28-36, dated November 30, 1990. If evidence of fuel leakage and/or water condensation is found while performing the initial or repetitive inspections, prior to further flight, purge and install a new vapor seal assembly in accordance with the Boeing service letter.

NOTE 1: The installation of a new vapor seal assembly does not terminate the requirement for the 1,500 flight hour repetitive inspection.

(b) For airplanes listed in Boeing Service Letter 737-SL-28-42, dated December 15, 1992, that are not subject to paragraph (a) of this AD: Within 90 days after the effective date of this AD, and thereafter at intervals not to exceed 1,500 flight hours, perform an inspection of the wing main tank float switch electrical conduits for fuel leakage and condensation build-up, in accordance with Boeing Service Letter 737-SL-28-36, dated November 30, 1990. If evidence of fuel leakage and/or water condensation is found while performing the initial or repetitive inspections, prior to further flight, purge and install a new vapor seal assembly in accordance with the Boeing service letter.

NOTE 2: The installation of a new vapor seal assembly does not terminate the requirement for the 1,500 flight hour repetitive inspection.

(c) Within 3 years after the effective date of this AD, install grease in the interior of the wing main tank float switch electrical conduits in accordance with Boeing Service Letter 737-SL-28-42, dated December 15, 1992, or 737-SL-28-42-A, dated July 15, 1993. Installation of grease in the conduits constitutes terminating action for the inspections required by paragraphs (a) and (b) of this AD.

(d) An 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.

NOTE 3: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO.

(e) Special 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.

(f) The inspections shall be done in accordance with Boeing Service Letter 737-SL-28-36, dated November 30, 1990. The installation shall be done in accordance with Boeing Service Letter 737-SL-28-42, dated December 15, 1992, or Boeing Service Letter 737-SL-28-42-A, dated July 15, 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 AirplaneDirectorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

(g) This amendment becomes effective on November 24, 1993.