AD 74-24-09

74-24-09 AIRESEARCH MANUFACTURING COMPANY OF ARIZONA: Amendment 39-2022 as amended by Amendment 39-2390. Applies to Ai-Research Model GTCP30-54, -59, -70 and -92 Auxiliary Power Units (APU's), installed in, but not limited to Hawker Siddeley HS and DH-125, Beech Hawker BH-125, Lockheed Model 1329, AMD-BA Falcon 20, Jet Commander 1121, Fairchild F-27, Goodyear Blimp, NAMC YS-11, BAC Viscount, HFB Noratlas, and Douglas DC-7 (conversion) certificated in all categories.

Compliance required as indicated to detect, correct and prevent turbine wheel hub separation, accomplish the following:

(a) APU serial numbers prior to 29046:

Within the next 25 hours of APU operating time in service after the effective date of Amendment 39-2022 (for Model GTCP30-92 APU's), or 25 hours of operating time in service after the effective date of the Amendment 39-2390 (for Models GTCP30-54, -59, and -70 APU's), unless previously accomplished, inspect the clearance between the turbine wheel and the stationary seal at a minimum of six (6) approximately equally spaced circumferential positions using a tool and procedures described in Paragraph 2.B and C. of AiResearch Service Bulletin GTCP30-49-3649, dated October 17, 1974, or later FAA-approved revisions. The clearance must be a minimum of 0.075 inch at each measured position. If clearance is less than minimum, the condition must be corrected before further operation.

(b) All serial number APU's:

Before exceeding 500 APU operating hours time in service, or, 50 hours of additional APU operating time in service after the effective date of Amendment 39-2022, whichever occurs later (for Model GTCP30-92 APU's only), or, before exceeding 500 APU operating hours time in service, or 50 hours of additional APU operating time in service from the effective date of Amendment 39-2390 (for Models GTCP30-54, -59, and -70 APU's), whichever occurs later, and at intervals not to exceed 500 hours of APU operating time in service thereafter, inspect the turbine wheel hub "saddle area" for presence of fatigue cracks. If cracks are detected, replace turbine wheel with a serviceable part before further operation. AiResearch Service Bulletin GTCP30-49-3649, dated October 17, 1974, or later FAA-approved revisions, describes an acceptable method of performing this inspection.

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

Amendment 39-2022 became effective November 29, 1974, for all persons except those to whom it was made effective by airmail letter dated November 8, 1974.

This amendment 39-2390 becomes effective November 19, 1975.