What happened
The flight originated in Wilmington, Delaware, with Rutland, Vermont, as the destination. Prior to departure, the pilot received weather briefings and was advised of flight precautions for icing and turbulence, along with pilot reports concerning icing conditions. After landing at an intermediate stop, the pilot informed Flight Service Station personnel that he had contacted Rutland and was told the weather was good, despite having previously diverted to Binghamton after learning Rutland's weather information was unavailable.
The pilot filed a flight plan and continued to Rutland. While approaching Rutland at 6,000 feet, he reported moderate icing. He requested and received clearance to climb to 8,000 feet but experienced difficulty climbing. He then requested and received vectors to Burlington, which had an overcast ceiling of 3,500 feet and good visibility.
While en route, the pilot was unable to maintain the minimum safe altitude of 5,500 feet and declared an emergency. After descending below the clouds, he stated that ice was shedding from the aircraft. He reported the runway in sight and was cleared to land. Witnesses observed that on final approach, the aircraft lost 150 to 200 feet of altitude, then regained some altitude several times. During a third loss of altitude, it hit the ground in a flat attitude and slid approximately 300 feet onto the runway.
The investigation
Post-accident examination revealed that the aircraft was not equipped for flight in known icing conditions. Investigators found the pitot heat switch in the off position. Additionally, a DC-9 crew reported a 15-knot loss of speed on final approach under similar conditions.