AD 75-05-17

75-05-17 AIRESEARCH MANUFACTURING COMPANY OF ARIZONA: Amendment 39-2108 as amended by Amendment 39-2224 is further amended by Amendment 39-2357. Applies to AiResearch Model GTCP660-4 and -4R APU's of the following listed serial numbers, installed in Boeing Model B-747 Series airplanes, unless modified to incorporate improved compressor assemblies in accordance with AiResearch Service Bulletin GTCP660-49-3039, Revision 1, 2, or 3, or later FAA approved revisions: Model GTCP660-4, S/N's P-37501 through P-37723 inclusive, and GTCP660-4R, S/N's P-101 through P-124 inclusive.

To prevent development of a hazardous condition during flight, accomplish the following:

(a) Prior to further flight, unless already accomplished, operators shall issue instructions to flight crews that the APU is not to be operated in flight. Within 72 hours after receipt of this Airworthiness Directive, unless already accomplished, install a placard in full view of the flight crew which reads:

"INFLIGHT OPERATION OF THE APU IS PROHIBITED."

(b) Prior to further flight, unless already accomplished, operators shall issue instructions to determine that damage hazardous to the aircraft has not occurred prior to flight after an automatic shutdown or manual shutdown to correct operating discrepancies of the APU after the completion of a successful APU start has been accomplished. This determination may be made by the following means:

(1) Inspect the APU and APU compartment for damage; or

(2) Inspect the exterior surfaces of the APU compartment for evidence of damage and verify that the APU turbine rotor can be rotated manually from the exhaust tailpipe; or,

(3) Perform the procedures described in Boeing Operations Manual Bulletin No. 75-1, dated January 17, 1975, or later FAA approved revision.

(c) The modifications and inspections described in AiResearch Bulletin GTCP660-49-3713, dated May 15, 1975, or later FAA-approved revisions must be incorporated on orbefore July 1, 1976. Upon completion of these modifications and inspections, the placard required by paragraph (a), above, may be removed and the inspections required by (b), above, may be discontinued.

(d) Equivalent procedures may be approved by the Chief, Aircraft Engineering Division, FAA Western Region, upon submission of adequate substantiating data.

Amendment 39-2108 supersedes the AD adopted January 10, 1975, and distributed by individual telegrams dated January 11, 1975.

Amendment 39-2108 was effective March 5, 1975 and was effective upon receipt for all recipients of the airmail letter dated January 22, 1975 which contained this amendment.

Amendment 39-2224 became effective June 5, 1975.

This amendment 39-2357 becomes effective October 6, 1975.