Cessna 177B N34880 accident near Neihart, Montana

Probable cause

The pilot's failure to maintain clearance from terrain while maneuvering at low altitude in turbulent conditions over mountainous terrain. Contributing to the accident was the pilot's improper decision to traverse the mountainous area with the airplane over its maximum gross weight and with a forward center of gravity.

NTSB analysis

While flying in mountainous terrain to show one of the passengers the area, the pilot entered a canyon that started to narrow as the canyon's walls rose so the pilot initiated a climb. The airplane then experienced a downdraft followed by a second downdraft, and the pilot found a low spot in the trees and attempted a climbing turn; however, the airplane would not climb and started brushing the trees. The airplane descended into the ground, and a postimpact fire ensued. The pilot reported no anomalies with the airframe or engine that would have precluded normal operation, and postaccident examination revealed no evidence of preimpact mechanical malfunctions or failures that would have precluded normal operation.

Weather charts revealed gusty wind conditions with vertical air mixing and an increased potential for turbulence in the accident area. Weather model soundings and simulations revealed that the layer from the surface through 10,000 feet mean sea level was unstable, indicating that the airplane likely encountered wind magnitudes as high as 30 knots, gusty winds, and updrafts and downdrafts in the mountainous terrain. Further, the airplane likely experienced turbulence and encountered downdrafts with a tailwind component at a velocity between 100 and 200 ft per minute.

Calculation of the airplane's weight and balance revealed that throughout the flight, the airplane was operating about 114 pounds over maximum gross weight and outside (forward) of the center of gravity envelope. It is likely that the airplane was unable to climb over the terrain as a result of the airplane's weight and balance configuration combined with the weather conditions in the area.

Text from the NTSB. Open the NTSB docket for WPR14FA362 for the full record.