What happened
The pilot of the aircraft had received a complete weather briefing the night before the flight and had reviewed updated weather information on the day of departure. To avoid an area of heavy precipitation, the pilot had modified the flight plan to change the intended route.
During the cruise phase of flight, the aircraft began to accumulate ice. Other aircraft operating along the same route reported encountering icing conditions at altitudes both above and below the altitude of the accident aircraft. As the rate of ice accumulation increased, the pilot requested clearance from air traffic control (ATC) to climb. However, the aircraft was unable to climb higher than approximately 8,000 feet MSL.
The accumulation became so severe that the heated windscreen could no longer maintain visibility. The pilot contacted ATC to request immediate vectors to the nearest airport and subsequently executed a precautionary landing. Upon arrival, the runway was covered in snow with a layer of ice beneath the snow. Because the windscreen remained iced over, the pilot's visibility was limited. During the landing roll, the aircraft slid off the runway and struck a snowbank, resulting in substantial damage to the aircraft. There were no injuries reported.
The investigation
A post-accident examination of the aircraft was conducted, which failed to reveal any mechanical anomalies. The investigation confirmed that the aircraft was properly equipped and certified for flight into known icing conditions.