Introduction
The accident occurred during an IFR departure when the pilot received progressive altitude clearances to climb to 15,000 feet. The aircraft, with the pilot as the sole occupant, experienced a loss of control leading to an inflight breakup. The pilot was killed.
Flight History
At 1607 EDT, the pilot was vectored for 'a good rate of climb' through 14,000 feet with clearance to proceed on course after leveling at 14,000 feet for 15,000 feet. Radar data indicated a steady climb until the aircraft was above 13,000 feet. As it climbed from 13,300 feet to 13,900 feet (the maximum recorded altitude), its speed slowed from about 115 knots to below 80 knots. At 1613 EDT, the pilot was cleared to proceed direct and change frequency.
Radar Data
Radar data showed that after reaching 13,900 feet, the aircraft deviated from course and entered a steep descent. Radar contact was lost and an inflight breakup occurred.
Wreckage
Pieces of wings and stabilizers were found up to 1.5 miles from the fuselage. A trajectory study disclosed the breakup occurred between 6,000 feet and 9,000 feet MSL. Examination of fractures on major components revealed characteristics typical of overstress; no preexisting cracks were found. No autopilot failure or bird strike was found.
Weather
Clouds were layered to 20,000 feet; the freezing level was about 12,500 feet. There was evidence the aircraft was in or near convective precipitation above the freezing level for about 1.5 minutes before the rapid descent.
Examination
The Pitot heat switch was found 'off' and the induction air door in its primary position.
Probable Cause
The official probable cause was the pilot's failure to use the airplane's ice protection equipment, which resulted in a performance loss due to induction icing, propeller icing, or both, while flying in convective instrument meteorological conditions (IMC) at and above the freezing level. The performance loss led to a stall, the recovery from which probably was exacerbated by the pilot's improper response to erroneous airspeed indications that resulted from blockage of the pitot tube by atmospheric icing.