The aircraft was parked at the airport 4 days prior to the flight. Aircraft parked nearby were snow covered. Although the preflight of the aircraft or takeoff was not witnessed, airport personnel said the pilot borrowed a broom to use for about 10 minutes. Fifteen minutes later the aircraft crashed. The aircraft struck the ground east of runway 16R in a left bank attitude, about halfway down the runway, where it touched down in snow covered grass. The aircraft travelled 298 feet across the ground before it struck a six-foot deep drainage ditch, located parallel and 227 feet from the runway, and erupted on fire. The examination of the aircraft did not disclose evidence of mechanical malfunction. Shortly after the accident, as part of the investigation, snow was removed from another aircraft parked near the accident aircraft. Ice was underneath the snow and could not be removed. The ramp area where the accident aircraft was parked was checked and airfoil shaped ice was found on the ground where the tail was positioned, but none where the wing was positioned.