Cessna 172 N6929H accident near Alpine, Utah

Probable cause

The pilot’s exceedance of the airplane’s critical angle-of-attack while maneuvering in a canyon, which resulted in a loss of airplane control.

NTSB analysis

The pilot and three passengers departed the airport for a daytime personal flight in favorable weather conditions. Radar data indicated the airplane flew on a southbound heading for about 25 minutes, steadily climbing to an altitude of 6,200 feet, before turning to the northeast and flying over a lake. The airplane continued on a north/northeast heading and climbed to an altitude of 8,785 feet over the next 16 minutes. It disappeared off radar 4 minutes later after performing a 270º turn in a canyon.

A witness in the area observed the airplane approach the canyon headed in a northwest direction and noted that he thought the airplane was too low to clear the terrain and depart the canyon. He observed the airplane enter a “tight, right banking turn” in the canyon. The airplane leveled off after turning about 180º, followed by a couple of left and right wing-tip oscillations before it entered a clockwise, corkscrew spin and disappeared from view in a vertical, nose-down attitude. The witness reported that the airplane’s engine was producing the same, constant sound until it started to vertically descend, and the noise started to oscillate.

Examination of the airplane and engine revealed no preimpact mechanical anomalies, and damage to the crankshaft flange and propeller was consistent with the engine producing power at the time of impact.

Additionally, autopsy and toxicology of the pilot did not reveal evidence of physiological impairment or incapacitation.

The radar data, witness statement, and damage to the airplane were all consistent with a loss of control after the pilot exceeded the airplane’s critical angle-of-attack while maneuvering in the canyon.

Text from the NTSB. Open the NTSB docket for WPR20LA203 for the full record.