What happened
Before departing Tucson, the pilot was advised of two marginal weather systems along his intended route. He took off at 1038 MST. At 1130, he contacted air traffic control (ATC) and reported being at 13,800 feet. From that point until 1214, his altitude varied between 10,000 feet and 16,000 feet. Radar contact was lost at 1228 while he was below 10,000 feet. At 1240, he reported being at 12,500 feet, then climbed to 14,500 feet to re-establish radar contact with ATC. Shortly thereafter, both radar and radio contact were lost.
School children observed the aircraft before it crashed. According to their accounts, the plane was in level flight at approximately 3,000 feet above ground level (7,000 feet mean sea level) when it pitched nose down, began spinning, and crashed. They did not see any debris separating from the aircraft prior to impact.
The investigation
An examination of the wreckage revealed that the left outboard wing panel and part of the left aileron had separated in flight. The outer portion of the left horizontal stabilator had folded upward. The wing panel was found 3.5 miles away with evidence it had failed up and aft.
Findings
There was evidence of moderate to severe turbulence in the vicinity of mountains. The pilot had been briefed on areas of turbulence, icing, precipitation, and deteriorating ceilings. The left outboard wing panel separation appears to be the primary structural failure. The moderate to severe turbulence likely contributed to the overstress leading to failure.
Safety message
Pilots should remain vigilant regarding weather conditions and turbulence forecasts, especially in mountainous terrain where localized severe weather can occur rapidly.