Cessna T210 N732MV accident near Silver City, Idaho

Probable cause

The pilot's failure to maintain adequate airspeed and his exceedance of the airplane’s critical angle of attack while making a turn in gusting wind conditions while flying through hilly terrain, which resulted in an aerodynamic stall.

NTSB analysis

The pilot and two passengers departed on a local area flight through mountainous terrain to a nearby airport. A review of primary targets that were consistent with the airplane’s flight track; initially, for a 3 minute period, the airplane was flying between 3,200 and 3,400 ft mean sea level (msl) at an average speed of 131 knots calibrated airspeed (KCAS). Radar data were lost for about the next 4 minutes due to mountainous terrain. Once the radar returns were picked up again, for about the next 4 minutes, the flight track showed the airplane continuing a southerly track, climbing from 4,700 to 6,500 ft msl. The last three radar returns showed that, during the last 36 seconds of flight, the airplane’s altitude above the ground decreased as the terrain rose such that the airplane was about 150 ft above ground level at the last radar return; the airspeed decreased to less than 70 KCAS by the end of the data. The wreckage was located near the bottom of a valley about 1,950 ft west and 15.5 nm east of the wreckage. Postaccident examination of the airplane and engine revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation.

Using the approximate conditions that existed at the time of the accident, including an estimated airplane gross weight of 3,900 lbs (about 100 lbs over the airplane’s maximum allowable gross weight) and flaps at 10°, the airplane’s stall speed was estimated to be about 68 KCAS. A ground scar at the accident site indicated that the left wing impacted terrain first, and the wreckage lay along a heading of 345°, indicating that the pilot was likely turning the airplane during the accident sequence. Given this evidence and that the airplane was losing speed as it climbed over rising terrain near the accident site and was approaching or at its stall speed by the end of the radar data, it is likely that the pilot did not maintain adequate airspeed while making a left turn in mountainous terrain. The gusting wind and low-level wind shear conditions could also contribute to the airplane exceeding its critical angle of attack, which resulted in an aerodynamic stall with the left wing low.

Although the pilot had type 2 diabetes, the accident circumstances are not consistent with incapacitation; therefore, it is unlikely that the pilot's diabetes contributed to the accident. Toxicology testing indicated that the pilot had taken buprenorphine, which can cause somnolence and impaired decision-making, at some point before the accident. However, based on the available information, it could not be determined whether the pilot's use of buprenorphine contributed to the accident.

Text from the NTSB. Open the NTSB docket for WPR18FA276 for the full record.