Cessna U206 N1738R accident near Rainy Pass, Alaska

Probable cause

The pilot's improper decision to continue the flight in deteriorating weather conditions, which resulted in an inadvertent entry into a box canyon and subsequent controlled flight into mountainous terrain.

NTSB analysis

The airline transport pilot was flying the airplane to a remote lodge to deliver cargo and return with passengers. The pilot and the chief pilot, who was also following the same route about 16 minutes later, had monitored the weather before and during the flight and recognized that the clouds were present but believed they could make the flight. The flight track data showed that the pilot flew at low altitudes as he flew into a winding valley leading toward a mountain pass. The chief pilot stated that, based on radio calls from the pilot, he was maneuvering around low clouds. The flight track showed that the accident airplane continued toward the mountain pass, then proceeded south past two mountain passes and into a box canyon. The airplane impacted steep mountainous terrain facing north, consistent with the pilot attempting a steep right turn to reverse course and exit the box canyon. Aviation weather cameras near the accident location showed low clouds and precipitation around the time of the accident. The chief pilot continued toward the destination but then elected to turn around as the low clouds hindered him from navigating through the valley. It is likely that the accident pilot encountered deteriorating weather as he flew through the valley toward mountainous terrain and attempted to exit the box canyon but was unable to maintain clearance from terrain as he performed the steep right turn. A postaccident examination of the engine, airframe, and recorded engine data did not reveal any anomalies that would have precluded normal operation.

Based on a review of the autopsy report and previous medical conditions, there was no evidence to suggest the pilot was impaired; therefore, the medical conditions were likely not a factor in this accident. Diphenhydramine was detected in the pilot's toxicology, but not quantified; therefore, the investigation was unable to determine if the pilot was impaired by diphenhydramine.

Text from the NTSB. Open the NTSB docket for CEN18FA386 for the full record.