AD 75-05-17
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Airesearch | The Boeing Company | Auxiliary Power Units | Airworthiness Directives; AIRESEARCH MANUFACTURING COMPANY OF ARIZONA: Applies to AiResearch Model GTCP660-4 and -4R APU's |
| aircraft | Airesearch | The Boeing Company | 747-100 Series | Airworthiness Directives; AIRESEARCH MANUFACTURING COMPANY OF ARIZONA: Applies to AiResearch Model GTCP660-4 and -4R APU's |
| aircraft | Airesearch | The Boeing Company | 747-100B Series | Airworthiness Directives; AIRESEARCH MANUFACTURING COMPANY OF ARIZONA: Applies to AiResearch Model GTCP660-4 and -4R APU's |
| aircraft | Airesearch | The Boeing Company | 747-100B SUD Series | Airworthiness Directives; AIRESEARCH MANUFACTURING COMPANY OF ARIZONA: Applies to AiResearch Model GTCP660-4 and -4R APU's |
| aircraft | Airesearch | The Boeing Company | 747-200B Series | Airworthiness Directives; AIRESEARCH MANUFACTURING COMPANY OF ARIZONA: Applies to AiResearch Model GTCP660-4 and -4R APU's |
| aircraft | Airesearch | The Boeing Company | 747-200C Series | Airworthiness Directives; AIRESEARCH MANUFACTURING COMPANY OF ARIZONA: Applies to AiResearch Model GTCP660-4 and -4R APU's |
| aircraft | Airesearch | The Boeing Company | 747-200F Series | Airworthiness Directives; AIRESEARCH MANUFACTURING COMPANY OF ARIZONA: Applies to AiResearch Model GTCP660-4 and -4R APU's |
| aircraft | Airesearch | The Boeing Company | 747-300 Series | Airworthiness Directives; AIRESEARCH MANUFACTURING COMPANY OF ARIZONA: Applies to AiResearch Model GTCP660-4 and -4R APU's |
| aircraft | Airesearch | The Boeing Company | 747-400 Series | Airworthiness Directives; AIRESEARCH MANUFACTURING COMPANY OF ARIZONA: Applies to AiResearch Model GTCP660-4 and -4R APU's |
| aircraft | Airesearch | The Boeing Company | 747-400D Series | Airworthiness Directives; AIRESEARCH MANUFACTURING COMPANY OF ARIZONA: Applies to AiResearch Model GTCP660-4 and -4R APU's |
Unsafe Condition
Development of a hazardous condition during flight due to APU operation.
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Required Actions
Issue flight crew instructions prohibiting in-flight APU operation and install a placard within 72 hours. Inspect APU and compartment for damage or verify turbine rotor rotation after shutdowns. Incorporate modifications and inspections per AiResearch Bulletin by July 1, 1976.
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Compliance Time
Prior to further flight, within 72 hours after receipt, and on or before July 1, 1976.
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Affected Aircraft
AiResearch Model GTCP660-4 (S/N P-37501-P-37723) and GTCP660-4R (S/N P-101-P-124) APU's installed in Boeing Model B-747 Series airplanes unless modified with improved compressor assemblies.
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Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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