Cessna 206 N50159 accident near Angoon, Alaska

Probable cause

The pilot's inadvertent turn toward terrain that was higher-than-expected while trying to avoid poor visibility conditions and his subsequent attempt to clear terrain, which reduced the airspeed and led to the exceedance of the airplane's critical angle of attack and an aerodynamic stall and spin.

NTSB analysis

The commercial pilot was conducting a commercial on-demand flight between two villages over open water in an amphibious float-equipped airplane before navigating through mountainous terrain. As the airplane approached the usual route company pilots took through the mountains, the accident pilot relayed to the operator's director of operations via airborne communications that he was unable to make it through the pass due to low clouds and reduced visibility and that he was going to try an alternate route over lower terrain. After the director of operations determined that the airplane did not arrive at its destination, search and rescue efforts ensued. The airplane was subsequently found in an area of rising steep mountainous, snow-covered terrain at an elevation of about 2,240 ft mean sea level in a near-vertical attitude.

A postaccident examination of the airframe and engine revealed no mechanical malfunctions or anomalies that would have precluded normal operation. GPS data for the accident flight showed the airplane making a total of five 360° turns in various locations in cloud-obscured, mountainous terrain while attempting to make it to the destination; the last turn was made shortly before impact. Based on the conversation the pilot had with the director of operations and the location of the wreckage, it is likely that the pilot thought he had taken a path over lower terrain but that he actually flew into a different valley which had higher-than-anticipated terrain, and then executed a 360° turn to gain altitude before continuing the flight. However, the airplane did not gain sufficient altitude to clear terrain, and it is likely that the pilot attempted another climb, which reduced the airspeed and led to the exceedance of the airplane's critical angle of attack. The disposition of the airplane at the accident site was consistent with an aerodynamic stall and a right spin.

Text from the NTSB. Open the NTSB docket for ANC16FA017 for the full record.