What happened
While operating under 14 CFR Part 135, the aircraft encountered unforecast icing as it approached its intended destination. The pilot reported that the windshield deicing plate failed to clear ice from its surface, resulting in the entire windshield becoming covered in ice. Due to these conditions, the pilot elected to divert to an alternate airport that offered superior instrument approach facilities.
During the second instrument approach, the pilot was guided to the runway by FAA air traffic control personnel positioned near the airfield. Upon touchdown, the aircraft made firm contact with the runway. During the subsequent landing roll, the left main gear collapsed, causing the aircraft to collide with runway edge lights and taxiway signs.
The investigation
An on-scene investigation examined the accumulation of ice on the aircraft. Investigators found approximately 1.5 inches of ice on the windshield. While the area covered by the windshield deicing plate was clear shortly after the aircraft came to a stop, the unbooted portions of the wings were found to have between 2 and 2.5 inches of ice accumulation.