AD 77-15-12
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| engine | Rolls-Royce Corporation | 250-B15A | DETROIT DIESEL ALLISON Model 250-B15 and B17 and 250-C18 and C20 Series Engines |
| engine | Rolls-Royce Corporation | 250-B15E | DETROIT DIESEL ALLISON Model 250-B15 and B17 and 250-C18 and C20 Series Engines |
| engine | Rolls-Royce Corporation | 250-B15G | DETROIT DIESEL ALLISON Model 250-B15 and B17 and 250-C18 and C20 Series Engines |
| engine | Rolls-Royce Corporation | 250-B17 | DETROIT DIESEL ALLISON Model 250-B15 and B17 and 250-C18 and C20 Series Engines |
| engine | Rolls-Royce Corporation | 250-B17B | DETROIT DIESEL ALLISON Model 250-B15 and B17 and 250-C18 and C20 Series Engines |
| engine | Rolls-Royce Corporation | 250-B17C | DETROIT DIESEL ALLISON Model 250-B15 and B17 and 250-C18 and C20 Series Engines |
| engine | Rolls-Royce Corporation | 250-B17D | DETROIT DIESEL ALLISON Model 250-B15 and B17 and 250-C18 and C20 Series Engines |
| engine | Rolls-Royce Corporation | 250-B17E | DETROIT DIESEL ALLISON Model 250-B15 and B17 and 250-C18 and C20 Series Engines |
| engine | Rolls-Royce Corporation | 250-B17F | DETROIT DIESEL ALLISON Model 250-B15 and B17 and 250-C18 and C20 Series Engines |
| engine | Rolls-Royce Corporation | 250-B17F/1 | DETROIT DIESEL ALLISON Model 250-B15 and B17 and 250-C18 and C20 Series Engines |
Unsafe Condition
Power turbine coupling nut failure due to corrosion.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Inspect the power turbine outer coupling nut P/N 6846278 in accordance with specified service letters. Replace the nut before further flight if unacceptable corrosion is found.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
Initial compliance within next 100 hours or 90 days from July 27, 1977, for engines with over 400 hours or one year since installation; within 500 hours or one year since installation for others. Repetitive inspections every 500 hours or one calendar year.
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Affected Aircraft
Rolls-Royce Corporation models 250-B15A, B15E, B15G, B17, B17B, B17C, B17D, B17E, B17F, etc., and 250-C18, C20 series engines with power turbine outer coupling nuts P/N 6846278 installed.
AI-generated summary from the source AD text. Verify against the official source before acting.
Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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