AD 90-21-09

90-21-09 BOEING: Amendment 39-6756. Docket No. 90-NM-49-AD.

Applicability: Model 747 series airplanes, except Model 747-400, line position 002 through 707, certificated in any category.

Compliance: Required as indicated, unless previously accomplished.

To prevent damage to air conditioning packs, wing fairing panels, and/or electrical wiring as a result of failure of crossover pneumatic ducts, accomplish the following:

A. Prior to the accumulation of 5,850 flight cycles, or within 4,000 flight cycles since last inspection and testing in accordance with Boeing Service Bulletin 747-36-2078, Revision 1, dated June 15, 1989, or within the next 1,850 flight cycles after the effective date of this AD, whichever occurs later, conduct a penetrant inspection, proof pressure test, and penetrant inspection again to detect cracks or ruptures of the crossover ducts, in accordance with the Accomplishment Instructions, Items A. through F., J., and K. of Boeing Service Bulletin 747- 36-2078, Revision 2, dated August 16, 1990. If cracks or ruptures are detected, prior to further flight, repair or replace in accordance with the service bulletin. The stress relieving procedure specified in Items G., H., and I. of the service bulletin may be accomplished in conjunction with the penetrant inspection and proof pressure testing required by this paragraph, and constitutes terminating action for the requirements of paragraph B. of this AD, for all crossover pneumatic ducts.

B. Prior to the accumulation of 3,000 flight cycles after accomplishment of the initial inspection required by paragraph A. of this AD, accomplish the following actions concurrently:

1. Conduct a penetrant inspection, proof pressure test, and penetrant inspection again to detect cracks or ruptures of the crossover ducts, in accordance with Items A. through F., J., and K. of the Accomplishment Instructions of Boeing Service Bulletin 747-36- 2078, Revision 2, dated August 16, 1990.If cracks or ruptures are detected, prior to further flight, repair or replace in accordance with the service bulletin.

2. Conduct stress relieving of the crossover ducts in accordance with Items G., H., and I. of the Accomplishment Instructions of Boeing Service Bulletin 747-36-2078, Revision 2, dated August 16, 1990.

C. Replacement of all ducts in accordance with Boeing Service Bulletin 747-36- 2078, Revision 2, dated August 16, 1990, constitutes terminating action for the requirements of this AD.

D. 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, FAA, Northwest Mountain Region.

NOTE: The request should be forwarded through an FAA Principal Inspector (PI), who will either concur or comment and then send it to the Manager, Seattle Aircraft Certification Office.

E. 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.

Amendment 39-6756, AD 90-21-09, becomes effective on November 9, 1990.