Flight Planning and Departure
At 1027, the pilot received a weather briefing for Holbrook, AZ. The briefer forecast "at least moderate icing in clouds or in precipitation above the freezing level" and stated, "I guarantee you moderate to severe turbulence" for the route. Later, the pilot obtained weather information for Amarillo, TX, and filed an IFR flight plan to Amarillo. The aircraft departed at 1150.
In-Flight Events
At 1204, the pilot reported an engine problem. Radar plots indicated a climb of about 500 feet per minute up to 11,200 feet. Thirty seconds later, the aircraft had descended to 8,500 feet. Radio and radar contact were lost around 1207.
Weather Conditions
A weather study concluded that probable meteorological conditions at the time and location of the accident included moderate to severe turbulence below 12,000 feet MSL. While in clouds above the freezing level, the aircraft likely encountered moderate to severe rime icing. The aircraft was not certificated for flight into known icing conditions.
Probable Cause
Official findings identified three occurrences: (1) in flight encounter with weather during climb to cruise, with findings of rain, turbulence in clouds, icing conditions, flight into known adverse weather initiated by the pilot-in-command, and operation with known deficiencies in equipment attempted by the pilot-in-command; (2) loss of control in flight during climb to cruise, with a finding of wing ice; (3) in flight collision with terrain/water during uncontrolled descent.