AD 78-26-01
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| engine | Rolls-Royce Corporation | 250-C28B | DETROIT DIESEL ALLISON Model 250-C28B Engines |
Unsafe Condition
Possible engine power loss resulting from electromagnetic interference.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Pull the N2 overspeed circuit breaker and secure it with tape or a Ty-Wrap. Install a placard stating 'Eng Ovsp Circuit Deactivated' near the breaker. Before February 1, 1979, modify the engine electrical system per Detroit Diesel Allison Commercial Engine Bulletin 73-2003, reactivate the N2 overspeed control, remove the 'Eng Ovsp Circuit Deactivated' placard, and remove the No. 4 plug from the N2 overspeed solenoid valve outlet vent if installed per CSL 2008.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
Before further flight and not later than February 1, 1979.
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Rolls-Royce Corporation Model 250-C28B engines installed in Bell Model 206L-1 rotorcraft certificated in all categories.
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
This site is not affiliated with or endorsed by the FAA. Always verify with official sources.