AD 91-18-05

91-18-05 BOEING: Amendment 39-8008. Docket No. 91-NM-61-AD.

Applicability: Model 747-400 series airplanes, listed in Boeing Service Bulletin 747-24- 2154, dated February 7, 1991, certificated in any category.

Compliance: Required within 180 days after the effective date of this AD, unless previously accomplished.

To prevent the loss of essential airplane electrical busses, accomplish the following:

A. Reroute and add protective sleeving to provide adequate separation between wiring associated with the differential protection current transformers for AC channels 1, 2, and 3, located in the P6 panel, in accordance with Boeing Service Bulletin 747-24-2154, dated February 7, 1991.

B. An alternative method 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 forwarded through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, 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.

D. The modification requirements shall be done in accordance with Boeing Service Bulletin 747-24-2154 dated February 7, 1991. 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. Copies may be inspected at the FAA, Northwest Mountain Region, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington, or at the Office of the Federal Register, 1100 L Street NW., Room 8401, Washington, D.C.

This amendment (39-8008, AD 91-18-05) becomes effective on September 20, 1991.