# AD 79-06-05: Overspeed Control System

- Type: Airworthiness directive
- Status: Current
- Products: Rolls-Royce 250-C28B and 250-C30
- Effective: March 26, 1979
- Superseded by: Nothing supersedes this AD
- Product type: Engine
- Amendment: 39-3436
- Registered aircraft: 435 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/D1A83C7E25BE719E862568270069147D.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/79-06-05

## The airworthiness directive

79-06-05 DETROIT DIESEL ALLISON: Amendment 39-3436. Applies to Model 250-C28B and 250-C30 engines with overspeed controls DDA P/N's 6895582 and 6894611 respectively, installed in but not limited to Bell 206L-1 and Sikorsky S-76 rotorcraft certificated in all categories. Compliance required as indicated, unless previously accomplished. To preclude possible engine power loss resulting from moisture in the overspeed control system, accomplish the following: (A) Before further flight, accomplish the following: (1) Pull the N2 overspeed circuit breaker and secure by wrapping with tape, or placing a Ty-Wrap around the breaker stem. (2) Install placard which states "Eng Ovsp Circuit Deactivated" in 3/16" or larger letters adjacent to N2 overspeed circuit breaker on Bell Model 206L-1 rotorcraft. On Sikorsky Model S-76 rotorcraft, install the placard on the panel which contains the N2 circuit breaker and on the panel which contains the N2 overspeed circuit test switch. The engine overspeed test outlined in the RFM will no longer function with the circuit breaker deactivated. (B) Not later than September 1, 1979, replace the affected engine overspeed controls with new engine overspeed controls DDA P/N's 23001750 for 250-C28 series engines and 23001751 for 250-C30 engines, unless previously accomplished. Concurrent with the accomplishment of this replacement, reactivate the N2 overspeed control by engaging the N2 overspeed circuit breaker and removing the placard "Eng Ovsp Circuit Deactivated." (Commercial Engine Bulletins CEB 73-2009 for the 250-C28 series engines and CEB 73-3006 for the 250-C30 engines also pertain to this subject.) This amendment becomes effective March 26, 1979.

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS E1GL](https://openairdocs.org/tcds/E1GL): Rolls-Royce Corporation; names 2 of 23 models: 250-C30, 250-C28B

## Registered aircraft it may apply to (OpenAirDocs)

Matched by airframe and engine model; the AD's applicability may narrow it by serial number, part number or equipment.

- Aircraft: 435 (0 by airframe model, 435 by engine model)
- Makers: Bell 224, MD Helicopters 68, Bell Helicopter Textron 53, Hiller 15, Mcdonnell Douglas Heli 13, Enstrom Helicopter 9, Sikorsky 8, Cessna 7, Beech 6, Hughes Helicopters 5

Models with the most aircraft:

- [Allison 250-C30 series](https://openairdocs.org/engine/allison-250-c30-series): 224 aircraft (engine model)
- [Allison 250 series](https://openairdocs.org/engine/allison-250-series): 79 aircraft (engine model)
- [Rolls-Royce 250-C30](https://openairdocs.org/engine/rolls-royce-250-c30): 76 aircraft (engine model)
- [Allison 250-C28 series](https://openairdocs.org/engine/allison-250-c28-series): 43 aircraft (engine model)
- [Allison 250-C30](https://openairdocs.org/engine/allison-250-c30): 5 aircraft (engine model)
- [Allison 250-C28B](https://openairdocs.org/engine/allison-250-c28b): 5 aircraft (engine model)
- [Rolls-Royce 250-C28B](https://openairdocs.org/engine/rolls-royce-250-c28b): 3 aircraft (engine model)

All 8 models: https://openairdocs.org/ad/79-06-05/models.md
Every aircraft: https://openairdocs.org/ad/79-06-05/aircraft.md

Its text cites no advisory circulars or STCs.

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