Beech 33 N873BC accident near Battleground, Washington

Probable cause

A failure of the throttle control assembly for reasons that could not be determined based on available evidence, which resulted in a runway overrun and impact with an obstacle.

NTSB analysis

The pilot selected the most favorable runway and flew his approach to land at his home airport. The airplane touched down normally near the runway threshold at the pilot's normal landing speed. Based on landing distance calculations, he should have been able to stop the airplane before the end of the runway. However, it was not until the airplane was about midfield that the pilot realized the airplane was not decelerating. At this point, the pilot attempted to reduce power further by twisting the knob of the throttle control counterclockwise, but the engine power did not decrease. As the airplane rapidly approached the end of the runway, the pilot used the mixture control to shut down the engine, but the airplane overran the runway end and the left wing impacted a pole, which resulted in substantial damage.

Postaccident examination of the airplane revealed no anomalies with the engine and most of the engine controls except for the throttle control. During engine runs, the throttle knob push button became intermittently stuck in a depressed position. Normally, turning the throttle knob counterclockwise from this position would reduce power; however, during the postaccident engine runs, a corresponding minor increase in power was observed. Although disassembly of the throttle mechanism revealed a loose nut in the throttle control assembly, it likely did not contribute to the throttle failure, as the nut would not have affected the knob’s use to make power adjustments. Further, the throttle control could still be manipulated by rotating the throttle knob during the postaccident engine run.

Based on the pilot's practices, it is likely that the pushbutton became partially depressed when the pilot reduced the engine power to descend while inbound to his home airport. When the pilot realized the airplane had not decelerated and attempted to make a minor power adjustment by rotating the throttle knob counterclockwise, the throttle control failed, and the pilot either experienced sustained or a subtle increase in engine power, which resulted in a runway overrun and impact with an obstacle. The reason for the failure of the throttle control assembly could not be determined based on available evidence.

Text from the NTSB. Open the NTSB docket for WPR19LA200 for the full record.