AD 58-02-03

58-02-03 HILLER: Applies to UH-12 Series Helicopters Equipped With Marvel- Schebler Automatic Altitude Compensating Carburetor Model MA-4-5AA (Aircooled P/N 19588).

Compliance required by June 1, 1958.

With a Marvel-Schebler Model MA-4-5AA carburetor installed, it is possible to start and run the engine with the carburetor mixture control in the idle cutoff position if the throttle is partially or fully opened. However, as soon as the throttle is fully closed, the idle cutoff will operate and shut off the engine. Therefore, it would be possible to start the engine, take off, and fly with the mixture in idle cutoff, as long as the throttle is never closed. The first time the throttle is closed, however, as in autorotation, an immediate engine stoppage would occur.

To prevent inadvertent engine stoppage in flight due to failure to place the carburetor mixture control in the "ALT.COMP" position before takeoff, the following measure is necessary:

Delete the carburetor mixture control from the cockpit and secure the carburetor setting at "ALT.COMP" at the carburetor.

Hiller will issue a service bulletin covering this subject. Appropriate FAA approved Helicopter Flight Manual revision required.