AD 90-22-01

90-22-01 BOEING: Amendment 39-6774. Docket No. 89-NM-20-AD.

Applicability: Model 757 series airplanes, listed in Boeing Alert Service Bulletin 757- 28A0017, Revision 2, dated January 4, 1989, certificated in any category.

Compliance: Required as indicated, unless previously accomplished.

To prevent engine flameout due to boost pump bypass valve freezing, accomplish the following:

A. Prior to the accumulation of 150 flight hours after May 4, 1988 (the effective date of Amendment 39-5895, AD 88-08-04), and thereafter at intervals not to exceed 300 flight hours, perform an operational test of the fuel boost pump bypass valves in accordance with Boeing Alert Service Bulletin 757-28A0017, dated February 11, 1988; or Part I of Revision 2, dated January 4, 1989; or Part I of Revision 3, dated April 26, 1990.

B. Within the next 4,000 hours time-in-service after the effective date of this amendment, modify the fuel boost pump bypass valves in accordance with PartII of Boeing Alert Service Bulletin 757-28A0017, Revision 2, dated January 4, 1989, or Revision 3, dated April 26, 1990. This constitutes terminating action for the repetitive tests required by paragraph A. of this AD.

C. 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.

D. 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 98055-4056.

Airworthiness Directive 90-22-01 supersedes AD 88-08-04, Amendment 39-5895. This amendment (39-6774, AD 90-22-01) becomes effective on November 21, 1990.