Background
Before departure, the pilot was advised of instrument meteorological conditions (IMC) along the initial portion of the route. The forecast included occasional moderate turbulence below 15,000 feet and mixed icing from the freezing level at 6,000 feet up to 18,000 feet. The pilot filed an IFR flight plan with a cruise altitude of 11,000 feet.
Flight and Accident
During departure, air traffic control cleared the pilot to climb to 9,000 feet and indicated that clearance to 11,000 feet would be issued approximately five minutes later. Radar data showed the aircraft climbing at about 1,500 feet per minute at a speed of 100 knots, with a slight deceleration above 8,000 feet. After reaching approximately 9,000 feet, the aircraft began to level off and accelerate. It then climbed momentarily, deviated laterally from its course, and entered a steep descent. An inflight breakup occurred, with wreckage scattered over an area of 4,100 feet. A trajectory study indicated that the breakup happened between 4,500 and 6,500 feet as the aircraft descended steeply at a speed exceeding 266 knots. Both occupants were killed.
Investigation
Metallurgical examination of the wings and stabilizers revealed features typical of overstress separation; no pre-existing cracks or defects were found. The aircraft had been recently purchased. The pilot's son noted that the principal problem was a 'twenty year leap in technology' from the previously owned PA-24, and that the pilot had difficulty with the avionics and flight director/autopilot, lacking detailed training in autopilot emergencies.
Probable Cause
The official probable cause is: The pilot's failure to activate the pitot heat before flying at and above the freezing level in instrument meteorological conditions (IMC), followed by his improper response to erroneous airspeed indications that resulted from blockage of the pitot tube by atmospheric icing. Contributing to the accident was spatial disorientation of the pilot.