AD 90-25-12

90-25-12 BOEING: Amendment 39-6821. Docket No. 90-NM-119-AD.

Applicability: Model 737 series airplanes, listed in Boeing Service Bulletin 737-35- 1033, dated March 15, 1990, certificated in any category.

Compliance: Required within 3,000 hours time-in-service after the effective date of this AD, unless previously accomplished.

To prevent fire caused by the chafing of wire bundles on crew oxygen system tubing, accomplish the following:

A. Inspect the clearances between the crew oxygen system tubing, the auxiliary power unit (APU) power feeder wire bundle, and the horizontal stabilizer trim control cables, located below the control cabin floor, in accordance with Boeing Service Bulletin 737-35-1033, dated March 15, 1990.

1. If there is inadequate clearance or damage has occurred, prior to further flight, repair the damage, replace the oxygen system tubing with modified tubing, and perform a leak check, in accordance with the Service Bulletin.

2. Ifclearance is inadequate between the crew oxygen tubing and the wire bundle only, and no damage has occurred, install floating loop clamps and spacers to obtain sufficient clearance between the tubing and the wire bundle, in accordance with the Service Bulletin.

B. An alternate means of compliance or adjustment of the compliance time, which provides an acceptable level of safety, may be used when approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate.

NOTE: The request should be submitted directly to the Manager, Seattle ACO, and a copy sent to the cognizant FAA Principal Inspector (PI). The PI will then forward comments or concurrence to the Seattle ACO.

C. Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes to a base in order to comply with the requirements of this AD.

All persons affected by this directive who have not already received the appropriate service documents from the manufacturer may obtain copies upon request to Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124. These documents may be examined at the FAA, Northwest Mountain Region, Transport Airplane Directorate, 1601 Lind Avenue S.W., Renton, Washington.

This amendment (39-6821, AD 90-25-12) becomes effective on January 7, 1991.