Aviat Aircraft Inc A N211AM accident near Herriman, Utah

Probable cause

The flight instructor's decision to conduct a low-altitude flight into a box canyon in high density altitude conditions and his failure to maintain airspeed while maneuvering to escape the canyon, which resulted in an exceedance of the airplane's critical angle of attack and an aerodynamic stall.

NTSB analysis

The flight instructor and pilot receiving instruction, departed on an instructional flight and proceeded toward mountainous terrain. A witness saw the airplane in a box canyon and reported that the airplane made a steep right turn and the nose dropped. To the witness, it appeared that the airplane was trying to escape the box canyon and that the speed of the airplane increased after the nose of the airplane dropped. The witness lost sight of the airplane behind terrain. Shortly thereafter, the witness saw smoke coming from the area where he had last seen the airplane. The wreckage was subsequently located by law enforcement personnel on down sloping terrain.

Examination of the airframe and engine revealed no preaccident mechanical anomalies that would have precluded normal operation.

The density altitude at the departure airport was 7,000 ft mean sea level (msl); the density altitude in the area of the accident site was over 10,000 ft msl. Given the high-density altitude it is likely that the airplane performance was decreased, and there was not enough engine power available for the airplane to climb out of the box canyon. It is also likely that as a result of the turn, the true airspeed increased the radius of the turn, and the pilot would have attempted to compensate and increased the bank angle and exceeded the airplanes critical angle of attack resulting in a stall.

Text from the NTSB. Open the NTSB docket for WPR17FA149 for the full record.