Cessna 150M N66255 accident near Russian Flat, Montana

Probable cause

The pilot's inadequate preflight performance planning and his operation of the airplane outside of the manufacturer's specified performance limitations, which resulted in his exceedance of the airplane's critical angle of attack and a subsequent aerodynamic stall/spin.

NTSB analysis

The commercial pilot attempted to take off from an uncontrolled grass runway with an uphill grade; the airplane subsequently impacted an open area of swamp land about 570 ft beyond the end of the runway. The airplane impacted in a right-wing, nose-low attitude; the impact damage was consistent with a near-vertical descent. Postaccident examination of the airframe and engine revealed no mechanical malfunctions or anomalies that would have precluded normal operation.

The density altitude at the time of the accident was calculated to be over 8,200 ft. Review of airplane manufacturer's takeoff performance charts revealed that the conditions present at the time of the accident exceeded the airplane's takeoff performance limitations. It is likely that, as the pilot attempted to take off uphill in high density altitude conditions, he exceeded the airplane's critical angle of attack, and the airplane experienced an aerodynamic stall/spin at low altitude.

Text from the NTSB. Open the NTSB docket for WPR14LA305 for the full record.