Mooney M20J N4474H accident near Dinsmore, California

Probable cause

The airplane’s degraded engine performance due to wear to the intake cam lobes, which diminished the airplane’s takeoff and climb performance, resulting in a subsequent collision with trees.

NTSB analysis

A witness who was near the departure airport reported observing the airplane circle the area, land on the runway, and stop at the midpoint of the runway. At that time, three people disembarked from the airplane, one of whom walked around the airplane. All three people then boarded the airplane, and the airplane taxied toward the approach end of the runway. The witness observed the airplane take off and stated that the airplane appeared to have rotated just short of the displaced runway threshold. The witness stated that the airplane “barely cleared the fence” and that the rotation was not smooth. Subsequently, the airplane impacted trees just beyond the departure end of the runway, where a postimpact fire ensued.

Postaccident examination of the engine revealed that the intake camlobes were worn and exhibited a rounded (instead of an elliptical) shape. The corresponding tappets for the intake cam lobes were galled. The alteration of the camlobe profile will in turn alter the amount and duration of the intake valves opening, thus negatively affecting power output. As a result, takeoff and climb performance would be directly affected. Although the extent of the degradation to the accident engine's power output could not be determined from the available evidence, the degradation was likely sufficient to cause a partial loss of engine power.

Text from the NTSB. Open the NTSB docket for WPR21FA272 for the full record.