Boeing A75N1(PT17) N75016 accident near Hollister, California

Probable cause

The improper installation of a relief valve spring that was shorter than the standard spring length, which slowed the response of the propeller governor to change the pitch of the blades during climbout, resulting in a partial loss of power.

NTSB analysis

The airplane was climbing out shortly after takeoff when the pilot noticed that the engine rpm was decreasing, and that the airplane was not gaining altitude. The pilot added that, even with the decrease in engine rpm, the engine was still producing some engine power. The pilot-rated passenger stated that the airplane was not gaining or losing altitude and that he verified that the propeller, throttle, and mixture control levers were in the correct settings. The pilot decided to maneuver away from power lines and make a forced landing onto a field. Subsequently, the lower part of both wings impacted the ground and sustained substantial damage.

A postaccident examined revealed that the propeller governor had a relief valve spring that was shorter in length than a standard relief valve spring. The shorter relief valve spring resulted in an internal governor pressure of 125 psi, which was less than the manufacturer’s setting of 180 to 200 psi. The lower internal pressure setting slowed the governor’s ability to make the immediate corrections in propeller blade pitch necessary to maintain the engine rpm during the climb out, which caused the engine to lose partial power.

Text from the NTSB. Open the NTSB docket for WPR21LA208 for the full record.