# AD 77-09-08: Bleed Valve Diaphragm

- Type: Airworthiness directive
- Status: Current
- Products: Rolls-Royce 250-B17, 250-B17B, 250-C20, 250-C20B and 250-C20C (T63-A-720)
- Effective: July 18, 1977
- Superseded by: Nothing supersedes this AD
- Product type: Engine
- Amendment: 39-2907
- Registered aircraft: 1,062 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/D9D3694C4DCD35E786256E120055AEBC.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/77-09-08

## The airworthiness directive

77-09-08 DETROIT DIESEL ALLISON: Amendment 39-2889 as revised by Amendment 39-2907. Applies to 250-C20, C20B, C20C, B17, B17B engines. Compliance required within the next 30 calendar days after the effective date of this AD, unless already accomplished. To prevent engine power loss resulting from bleed valve diaphragm failure, accomplish the following: Clip lockwire and remove the exit nozzle P/N 6874818 from the bleed valve cover. Using a small screwdriver install strainer assembly P/N 6896347 in the valve cover exit port until it is fully seated. Install the exit nozzle in the bleed valve cover. Tighten to 35-45 lb. in. CAUTION: DO NOT EXCEED 45 LB. IN.; OVERTIGHTENING MAY DAMAGE THE STRAINER. Approximately 2-3 threads of the exit nozzle will be visible when the strainer assembly is seated fully in the bleed valve. If more than three threads are visible this modification must not be accomplished and bleed valve must be removed for overhaul. To clear the bleed valvecover passages of burrs and other particles, again remove the exit nozzle and strainer assembly from the valve cover. With the throttle at IDLE CUT OFF, motor the engine in excess of 10% rpm. Using a small screwdriver, reinstall the strainer in the valve cover exit port until it is fully seated. Reinstall the exit nozzle in the bleed valve cover. Tighten to 35-45 lb. in. CAUTION: DO NOT EXCEED 45 LB. IN.; OVERTIGHTENING MAY DAMAGE THE STRAINER. Approximately 2-3 threads of the exit nozzle will be visible when the strainer is fully seated in the bleed valve. Secure the exit nozzle with lockwire. (Detroit Diesel Allison Commercial Engine Bulletins No. 1116 for the 250-C20 series and No. 1071 for the 250-B17 series engines also pertain to this subject.) Amendment 39-2889 became effective June 10, 1977. This amendment 39-2907 becomes effective July 18, 1977.

## Affected data sheets (2) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS E4CE](https://openairdocs.org/tcds/E4CE): Rolls-Royce Corporation; names 3 of 23 models: 250-C20, 250-C20C (T63-A-720), 250-C20B
- [TCDS E10CE](https://openairdocs.org/tcds/E10CE): Rolls-Royce Corporation; names 2 of 11 models: 250-B17B, 250-B17

## 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: 1,062 (0 by airframe model, 1,062 by engine model)
- Makers: Bell 565, Hughes Helicopters 145, Mcdonnell Douglas Helicopter 79, MD Helicopters 44, Hughes 35, Hiller 23, Agusta 21, Bell Helicopter Textron 20, Messerschmitt-Bolkow-Blohm 13, Aerospatiale 12

Models with the most aircraft:

- [Allison 250-C20 series](https://openairdocs.org/engine/allison-250-c20-series): 530 aircraft (engine model)
- [Rolls-Royce 250-C20B](https://openairdocs.org/engine/rolls-royce-250-c20b): 215 aircraft (engine model)
- [Allison 250-C20B](https://openairdocs.org/engine/allison-250-c20b): 113 aircraft (engine model)
- [Allison 250 series](https://openairdocs.org/engine/allison-250-series): 79 aircraft (engine model)
- [Allison 250-C20](https://openairdocs.org/engine/allison-250-c20): 54 aircraft (engine model)
- [Rolls-Royce 250-C20](https://openairdocs.org/engine/rolls-royce-250-c20): 42 aircraft (engine model)
- [Allison 250-B17 series](https://openairdocs.org/engine/allison-250-b17-series): 14 aircraft (engine model)
- [Allison 250-C20C](https://openairdocs.org/engine/allison-250-c20c): 9 aircraft (engine model)
- [Rolls-Royce 250-C20C](https://openairdocs.org/engine/rolls-royce-250-c20c): 6 aircraft (engine model)

All 11 models: https://openairdocs.org/ad/77-09-08/models.md
Every aircraft: https://openairdocs.org/ad/77-09-08/aircraft.md

Its text cites no advisory circulars or STCs.

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