Pre-Accident Flight
Approximately 3 minutes before the accident, the airplane was flying northeast at 17,100 feet. Air traffic controllers instructed the pilot to contact Boston Center. The pilot acknowledged, and no further transmissions were received. Radar data showed the airplane continued level at 17,100 feet on a northeasterly heading, maintaining a groundspeed of 255 knots for about 2 minutes after the last transmission.
Loss of Control
The airplane then climbed 300 feet and descended abruptly, losing 10,700 feet over 46 seconds while maintaining an approximate ground speed of 255 knots. Subsequently, it climbed from 6,700 feet to 7,600 feet, held that altitude for 4 seconds, and then entered a continuous descent until the last radar contact 17 seconds later at 2,400 feet.
Witness Observations
Several witnesses observed the airplane before it impacted the ground. All described the airplane in a "flat spin" with the engines running prior to impact.
Weather Conditions
Recorded weather data revealed several areas of light-to-moderate precipitation echoes near the accident site. Maximum echo tops ranged from 14,000 to 25,000 feet, with tops near 17,000 feet in the immediate vicinity. Radar images showed the airplane traveling through an area of lower echoes for about 5 minutes before the accident. AIRMET Zulu was current for icing conditions from the freezing level to 22,000 feet over the route and accident site. Four PIREPs indicated light-to-moderate rime to mixed icing in clouds from the freezing level to 16,000 feet. Two aircraft reported cloud tops from 16,000 to 17,000 feet.
Examination Findings
Examination of the airplane and engines revealed no pre-impact mechanical anomalies. The cockpit overhead switch panel showed propeller de-ice, engine intake heat, windshield anti-ice, and wing de-ice were all in the 'off' position. Toxicology tests detected pseudoephedrine and diphenhydramine in the pilot's urine; diphenhydramine was not detected in the blood.