What happened
During a night arrival in fog and drizzle, the pilot was cleared for an ILSS runway 1L approach. While executing the approach, the pilot reported encountering moderate rime ice. Radar data indicated that the aircraft remained inbound on the localizer until it reached the vicinity of the middle marker. At that point, the aircraft deviated approximately 20 degrees to the left and struck the ground about 300 feet short and 300 feet left of the runway threshold.
Witnesses at the scene reported that the airplane appeared to stop its descent and slow down shortly before entering a steep descent and a spin.
The investigation
An on-scene investigation found no anomalies regarding the airframe, control systems, or powerplant prior to the impact. However, investigators identified 1/4 inch of ice on the wing leading edges, along with a 1/2 inch high ridge of ice located approximately 3 inches aft of the deicing boots, running parallel to them. The cockpit and windshield heating systems were found in the 'off' position.
While company records indicated the pilot had passed a 14 CFR Part 135 checkride on May 20, 1994, signed by the chief pilot, other available information suggested the chief pilot would not have been able to have conducted the checkride on that specific date. The pilot's logbook was unavailable for inspection.