What happened
While operating under IFR clearance, the aircraft type was climbing through a series of cloud layers between 4,000 and 13,000 feet. At the time of the accident, an AIRMET was active for moderate rime and mixed icing below 18,000 feet. As the plane attempted to intercept a victor airway at a climb rate of 2,000 feet per minute, it began performing erratic altitude and heading changes that deviated from ATC instructions. The aircraft performed a series of turns and climbs/descents before entering a rapid right-hand descent at 8,500 feet.
During the descent through 7,000 feet, the pilot transmitted a distress message indicating a loss of instrument guidance. The final radar contact showed the aircraft descending through 3,200 feet at a rate of approximately 11,000 feet per minute, near its maximum operating speed. Witnesses on the ground observed the plane emerging from the clouds in a high-speed spiral before the aircraft broke up at approximately 1,000 feet AGL. There were 0 fatalities reported in the provided text, though the aircraft was destroyed.
Findings
Investigation of the wreckage determined that all structural failures were caused by aerodynamic overload. While the aircraft was equipped for flight into known icing conditions, a discrepancy was found in the pitot heat configuration. The right pitot heat switch was in the ON position, but the left switch was in the OFF position.
Technical analysis of the left pitot heat switch revealed that the housing had a pre-existing fracture. This fracture allowed for the accumulation of large, coarse, fibrous lint-like debris inside the component. This debris, combined with dirty electrical contacts and broken conductor strands, caused the left pitot heat switch to provide intermittent electrical contact, preventing reliable operation of the heating element.