What happened
On May 1, 2017, a Cessna 208B, registration N803TH, crashed into a steep, snow-covered mountain in the Alaska Peninsula National Wildlife Refuge. The flight was being operated by Grant Aviation, Inc., as a non-scheduled mail contract flight.
The aircraft departed Port Heiden Airport (PAPH) at 1325 for Perryville Airport (PAPE). The route required traversing the Aleutian Peninsula, crossing mountainous terrain with elevations between 2,900 ft and 4,600 ft. During the first segment of the day's scheduled route, a passenger noted that the pilot flew lower than usual and through clouds due to low visibility.
At approximately 1353, the company was notified that the US Coast Guard had detected an emergency locator transmitter (ELT) signal from the aircraft. A recovery mission later located the wreckage about 24 miles northeast of Plausible destination, 2,993 ft above mean sea level. The pilot sustained 1 fatal injury.
The investigation
Investigators examined the wreckage and found the site was consistent with an impact during a left turn. The aircraft was equipped with a terrain awareness and warning system (TAWS) that was not inhibited at the time of the crash, though it could not be determined if the pilot received or responded to any alerts. The aircraft lacked flight tracking equipment or a flight data recorder.
Mechanical examination of the engine and airframe revealed no anomalies that would have prevented normal operation. While the company had been monitoring a recurring chip detector light in the engine, no mechanical failure was identified as a cause of the crash.
Weather analysis showed that the area was experiencing mountain obscuration, overcast clouds, and likely rain showers. Satellite and weather camera imagery indicated that the conditions were likely to result in "flat light," an optical illusion that can obscure terrain features and depth perception.
Findings
- The pilot was conducting a visual flight rules (VFR) flight in an area characterized by mountainous terrain and instrument meteorological conditions (IMC).
- The presence of snow-covered terrain and heavy cloud cover likely created flat light conditions, preventing the pilot from recognizing the proximity of the mountain during a turn.
- The company's flight risk assessment process was inadequate, as it relied on outdated weather observations and failed to account for en route hazards or active AIRMETs for mountain obscuration.
- The company failed to provide the pilot with required recurrent CFIT-avoidance simulator training, as his last session had occurred 15 months prior to the accident.