Air Tractor Inc AT-802A N802NZ accident near Estes Park, Colorado

Probable cause

The airplane’s encounter with severe to extreme turbulence associated with mountain wave rotor cloud activity, which resulted in loss of airplane control.

NTSB analysis

The aerial firefighting flight was approaching the intended drop location when the airplane rolled inverted, descended, and impacted terrain. The airplane wreckage displayed features of a low-speed, nose-down impact with the engine producing power. The airplane sustained substantial damage to the fuselage, wings, and empennage. Recorded data showed decreasing indicated airspeed and increasing engine power toward the end of the flight. Postaccident examination of the airplane revealed no mechanical anomalies that would have precluded normal operation.

The accident site was located on the eastern slope of a high mountain range, and west winds gusting to near 30 knots were reported near the time of the accident. An animation of satellite imagery showed that most of the clouds west and east of the accident site did not propagate eastward with time with the mean wind but remained relatively stationary, which was consistent with mountain wave activity. Low cloud bands immediately south of the accident also remained relatively stationary and were likely rotor clouds, a type of cloud associated with severe or greater turbulence. It is likely the airplane encountered severe to extreme low altitude turbulence associated with rotor clouds, which resulted in the loss of control.

Text from the NTSB. Open the NTSB docket for CEN22FA035 for the full record.