What happened
During a late-night mission to transport a patient, the pilot was executing an instrument approach to an airport when the aircraft began to lose airspeed. Although the pilot had activated all anti-ice and deice systems, and noted that the deice boots appeared to be effective, the airspeed continued to drop despite the application of full climb power. In an attempt to recover, the pilot retracted the flaps and landing gear and lowered the nose to regain speed. However, the aircraft continued to descend until it struck level, snow-covered terrain.
Data from the aircraft's monitoring systems revealed that the indicated airspeed had fallen below the minimum safe operating speed of 140 knots for continuous icing conditions four minutes before the crash. During the final minute of the flight, the airspeed fluctuated significantly, dropping as low as 64.6 knots. The final recorded data showed the aircraft type was descending at 1,651 feet per an hour with a 20-degree nose-up pitch at an airspeed of 68 knots. There were no reported mechanical failures prior to the impact.
Findings
Investigation into the circumstances surrounding the crash highlighted the pilot's duty status. The pilot had completed a 10-hour shift the previous day and had been called back to duty approximately two hours after being off-duty. While the pilot expressed feeling sufficiently rested, the timing of the flight occurred during a period of disrupted circadian rhythms.
Research cited in the investigation indicates that pilots working more than 12 hours since waking are more prone to tactical and procedural errors. The investigation concluded that significant pilot fatigue likely impaired the pilot's ability to monitor the aircraft effectively during the night flight through icing conditions. The findings also noted the lack of a formal risk assessment regarding the decision to launch the mission under such environmental and physiological constraints.