Cessna 172 N5660J accident near Afton, Wyoming

Probable cause

The pilot’s failure to maintain terrain clearance after an encounter with a downdraft while maneuvering in a valley with a high-density altitude, which resulted in impact with trees and terrain.

NTSB analysis

An airline transport pilot and two passengers departed on an aerial observation flight in mountainous terrain. While flying in a valley, the pilot reported that he experienced downdrafts, which made it unlikely that the airplane would clear the ridge lines in front of the airplane. The pilot performed a steep 180° left turn to exit from the high terrain. However, after completing the turn, the airplane was unable to climb over terrain and struck several trees before impacting the ground, which resulted in substantial damage to the wings and fuselage.

The pilot reported no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.

The airplane's weight and balance was calculated as about 256 pounds below the maximum gross weight limit, and the density altitude at the accident was calculated as about 8,765 ft mean sea level (msl). A weather study of the accident area identified no significant winds, turbulence, or low-level wind shear present or forecast. The study did identify a surface-based inversion that existed to about 500 ft above ground level (agl). Additionally, another pilot in a different airplane stated that moderate turbulence was present near the accident area about 18 minutes before the accident.

Due to a combination of the airplane's high gross weight, a high-density altitude, a temperature inversion, maneuvering at a steep bank in order to avoid high terrain, and with potential downdrafts, the pilot dissipated the airplane's airspeed and altitude, and approached a stall. With no altitude available to increase the airspeed after the left turn and already at full power, the airplane continued to descend until it struck trees and impacted terrain.

Text from the NTSB. Open the NTSB docket for WPR18LA241 for the full record.