AD 91-06-08

91-06-08 BOEING: Amendment 39-6928. Docket No. 90-NM-27-AD.

Applicability: Model 747 series airplanes, line positions 2 through 707, except Model 747-400 series airplanes, certificated in any category.

Compliance: Required as indicated, unless previously accomplished.

To prevent damage to wing panels and/or electrical wiring as a result of failure of wing leading edge ducts, accomplish the following:

A. Prior to the accumulation of 5,850 flight cycles, or within the next 1,850 flight cycles after the effective date of this AD, whichever occurs later, conduct a penetrant inspection and proof pressure test as follows:

1. For titanium T-ducts and flanged ducts: Conduct the inspection and test in accordance with the Accomplishment Instructions, Items A. through F., J., and K. of Boeing Alert Service Bulletin 747-36A2074, Revision 3, dated May 11, 1989, or Revision 4, dated September 13, 1990. If cracks or ruptures are detected, prior to further flight, repair or replace the duct in accordance with the service bulletin.

2. For flangeless ducts: Conduct the inspection and test in accordance with the Accomplishment Instructions, Items A. through F., J., and K. of Boeing Alert Service Bulletin 747- 36A2074, Revision 4, dated September 13, 1990. If cracks or ruptures are detected, prior to further flight, repair or replace the duct in accordance with the service bulletin.

NOTE: For both flanged and flangeless ducts specified in paragraphs A.1. and A.2. of this AD (excluding T-ducts): The duct weld stress relieving procedure specified in Items G., H., and I. of the referenced service bulletins (and required by paragraphs B.2. and B.3. of this AD) may be accomplished in conjunction with the penetrant inspection and proof pressure test required by this paragraph, and constitutes terminating action for the requirements of paragraphs B.2. and B.3. of this AD.

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:

1. For titanium T-ducts: Replace titanium T-ducts with Inconel T-ducts in accordance with Boeing Service Bulletin 747-36-2059, dated June 3, 1983. Accomplishment of this replacement constitutes terminating action for the requirements of this AD.

2. For flanged ducts, except T-ducts: Conduct a penetrant inspection, proof pressure test, and duct weld stress relieving in accordance with the Accomplishment Instructions, Items A. through K., of Boeing Alert Service Bulletin 747-36A2074, Revision 3, dated May 11, 1989, or Revision 4, dated September 13, 1990. If cracks or ruptures are detected, prior to further flight, repair or replace the duct in accordance with the service bulletin. If the duct weld stress relieving has already been accomplished in accordance with AD 88-17-07 prior to the effective date of this AD, it constitutes terminating action for the requirements of this paragraph for flanged ducts.

3. For flangeless ducts: Conduct a penetrant inspection, proof pressure test, and duct weld stress relieving in accordance with the Accomplishment Instructions, Items A. through K., of Boeing Alert Service Bulletin 747-36A2074, Revision 4, dated September 13, 1990.

If cracks or ruptures are detected, prior to further flight, repair or replace the duct in accordance with the service bulletin. If the penetrant inspection, proof pressure test, and duct weld stress relieving have already been accomplished in accordance with AD 88-17-07 prior to the effective date of this AD, the following apply:

a. For straight flangeless ducts (L3, R3, L4, R4, L5, and R5 defined in the service bulletin): The above constitutes terminating actions for the requirements of this AD.

b. For bent flangeless ducts (L2, R2, L7, and R7 defined in the service bulletin): Conduct only a proof pressure test in accordance with Boeing Alert Service Bulletin 747- 36A2074, Revision 4, dated September 13, 1990.

C. For ducts other than T-ducts: Replacement of all leading edge pneumatic ducts by kits in accordance with Boeing Alert Service Bulletin 747-36A2074, Revision 3, dated May 11, 1989, or Revision 4, dated September 13, 1990; or in accordance with Boeing Service Bulletin 747-36-2092, dated June 28, 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 (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.

E. Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes to a base inorder 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 SW., Renton, Washington.

Airworthiness Directive 91-06-08 supersedes AD 88-17-07, Amendment 39-5986.

This amendment (39-6928, AD 91-06-08) becomes effective on April 15, 1991.