39. A precaution for the operation of an engine equipped with a constant-speed propeller is to

On aircraft equipped with a constant-speed propeller, the throttle controls the engine power output which is registered on the manifold pressure gauge. The propeller control changes the pitch angle of the propeller and governs the RPM which is indicated on the tachometer. On most airplanes, for any given RPM, there is a manifold pressure that should not be exceeded. If an excessive amount of manifold pressure is carried for a given RPM, the maximum allowable pressure within the engine cylinders could be exceeded, thus putting undue strain on them.