AD 74-11-03

74-11-03 AIRESEARCH: Amendment 39-1848. Applies to model GTCP36-4A, -6, -16, and -28 Auxiliary Power Units (APU) installed on, but not limited to, Grumman Gulfstream 1159, Fokker F-28, NAMC YS-11, and VFW Fokker 614 Aircraft.

"Pursuant to the authority of the Federal Aviation Act of 1958, delegated to me by the Administrator (31 F.R. 13697), the following airworthiness directive applicable to all aircraft incorporating AiResearch Model GTCP36-4A, -6, -16, and -28 Auxiliary Power Units (APU), installed in, but not limited to, Grumman Gulfstream 1159, Fokker F-28, NAMC YS-11, and VFW Fokker 614 aircraft, listed in AiResearch Alert Service Bulletins GTCP36-49-A3621, dated March 19, 1974, and GTCP36-49-A3618, dated April 1, 1974, or later FAA-approved revisions, is effective immediately upon receipt of this airmail letter. This AD is required due to a manufacturing error resulting in a certain lot of fuel controls for the APU containing a case casting wall thickness below allowable design limits. As the vessel is a high pressure cavity, failure of the wall would allow H.P. fuel to leak into the APU compartment. Compliance required as indicated, unless already accomplished.

Within 25 hours additional time in service of any aircraft on which the APU is installed, visually inspect the APU fuel control body per AiResearch Alert Service Bulletins GTCP36-49-A362l, dated March 19, 1974, or GTCP36-49-A3618, dated April 1, 1974, or later FAA-approved revisions. Prior to the installation of any AiResearch APU models listed herein, in any aircraft, conduct the visual inspection per the applicable Alert Service Bulletins. If, as a result of any of the foregoing inspections, fuel control units are found to have the unacceptable case casting wall thickness, either:

(A) Prior to further flight, placard the APU inoperative until replaced with a new or serviceable part. The APU may not be operated until a new or serviceable part is installed. or

(B) Replace, prior to further flight, with a new or serviceable part. Mark all fuel control units found to be unacceptable in a conspicuous manner to prevent inadvertent return to service. Return said units to AiResearch for exchange as indicated in the AiResearch Alert Service Bulletins. Re-identify acceptable units per the Alert Service Bulletins. Make appropriate aircraft logbook entries to reflect compliance with this AD. Aircraft may be flown to a base for performance of maintenance required by this AD, per FAR's 21.197 and 21.199, provided that the APU is inoperative for said flight."

This amendment is effective May 20, 1974, for all persons except those to whom it was made effective immediately by airmail letter dated April 25, 1974.