Amateur-built N595KF accident near Lander, Wyoming

Probable cause

The inexperienced pilot’s exceedance of the airplane’s critical angle-of-attack during a turn at high density altitude, which resulted in an accelerated stall and impact with water. Contributing to the accident was the pilot’s poor judgment to continue the flight despite the airplane’s limited performance during the accident flight.

NTSB analysis

The sport pilot departed in the experimental, amateur-built airplane from a high-altitude airport with a passenger toward a mountain range. Due to the airplane’s performance limitations in the high-altitude environment, the pilot was forced to circle twice as he climbed. After he entered the mountain range, he completed a circling descent to about 500 ft above ground level (agl) to overfly a lake located about 8,500 ft mean sea level (msl). The pilot then flew southwest over the lake at the planned altitude but encountered turbulence and downdrafts that forced the airplane to descend to about 25 ft agl. He applied full throttle to build airspeed and to climb, but the airplane did not climb. The pilot was forced to perform a left turn to avoid rising terrain to his right and obstacles ahead of him. However, during the maneuver, the airplane pitched up and turned left. It then immediately entered a nose-down attitude, consistent with an accelerated stall, and impacted the water.

Postaccident examination of the airframe and engine revealed no mechanical anomalies. Density altitude at the lake was about 9,500 ft. There were no charts to compute the airplane’s performance at 8,500 ft mean sea level but based on the pilot’s recollection of how the airplane was flying, the airplane’s climb performance was likely degraded at the density altitude he was operating. Any downdrafts would have further inhibited the airplane from a climb. The pilot likely exceeded the airplane’s critical angle-of-attack when he initiated a climbing left turn in such conditions.

The pilot had limited practical experience flying in mountain environments and his most recent training took place about 1 year prior. These factors likely contributed to his poor judgment in choosing to continue the planned flight to a low altitude in a high-density altitude mountain environment despite the airplane’s deficient rate of climb.

Text from the NTSB. Open the NTSB docket for WPR20LA170 for the full record.