AD 75-11-04
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| engine | Pratt & Whitney Canada Corp. | PT6A-20 | UNITED AIRCRAFT Model PT6A-6, -6A, -6B, -6/C20, -20, -20A, -20B, -27, -28, -34 Series Engines and PT6B-9 Engines |
| engine | Pratt & Whitney Canada Corp. | PT6A-20A | UNITED AIRCRAFT Model PT6A-6, -6A, -6B, -6/C20, -20, -20A, -20B, -27, -28, -34 Series Engines and PT6B-9 Engines |
| engine | Pratt & Whitney Canada Corp. | PT6A-20B | UNITED AIRCRAFT Model PT6A-6, -6A, -6B, -6/C20, -20, -20A, -20B, -27, -28, -34 Series Engines and PT6B-9 Engines |
| engine | Pratt & Whitney Canada Corp. | PT6A-27 | UNITED AIRCRAFT Model PT6A-6, -6A, -6B, -6/C20, -20, -20A, -20B, -27, -28, -34 Series Engines and PT6B-9 Engines |
| engine | Pratt & Whitney Canada Corp. | PT6A-28 | UNITED AIRCRAFT Model PT6A-6, -6A, -6B, -6/C20, -20, -20A, -20B, -27, -28, -34 Series Engines and PT6B-9 Engines |
| engine | Pratt & Whitney Canada Corp. | PT6A-34 | UNITED AIRCRAFT Model PT6A-6, -6A, -6B, -6/C20, -20, -20A, -20B, -27, -28, -34 Series Engines and PT6B-9 Engines |
| engine | Pratt & Whitney Canada Corp. | PT6A-6 | UNITED AIRCRAFT Model PT6A-6, -6A, -6B, -6/C20, -20, -20A, -20B, -27, -28, -34 Series Engines and PT6B-9 Engines |
| engine | Pratt & Whitney Canada Corp. | PT6A-6A | UNITED AIRCRAFT Model PT6A-6, -6A, -6B, -6/C20, -20, -20A, -20B, -27, -28, -34 Series Engines and PT6B-9 Engines |
| engine | Pratt & Whitney Canada Corp. | PT6A-6B | UNITED AIRCRAFT Model PT6A-6, -6A, -6B, -6/C20, -20, -20A, -20B, -27, -28, -34 Series Engines and PT6B-9 Engines |
| engine | Pratt & Whitney Canada Corp. | PT6A-6/C20 | UNITED AIRCRAFT Model PT6A-6, -6A, -6B, -6/C20, -20, -20A, -20B, -27, -28, -34 Series Engines and PT6B-9 Engines |
Unsafe Condition
Failure of the reduction gearbox in engines incorporating power turbine shaft housing assembly part number 3010548, which could lead to engine distress.
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Required Actions
Install magnetic chip detector part number 3014794 or 3019373 with new preformed packing, torque to 45 to 55 lb. in., and lockwire. Install cap or connector with electrical wiring leading to an accessible area. Check magnetic chip detector every 25 hours in service for electrical continuity using an ohmmeter; if resistance ≤100 ohms, clean detector and inspect main engine oil filter per AD 75-06-01.
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Compliance Time
For PT6A-20, -20A, -20B, -6/C20 engines: within 50 hours in service after May 20, 1975. For PT6A-6, -6A, -6B, -27, -28, -34 and PT6B-9 engines: at next engine overhaul shop visit, but no later than 3500 hours in service after May 20, 1975.
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Affected Aircraft
Pratt & Whitney Canada Corp. PT6A-6, -6A, -6B, -6/C20, -20, -20A, -20B, -27, -28, -34 series engines and PT6B-9 engines with power turbine shaft housing assembly part number 3010548.
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Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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