What happened
On May 6, 1971, an Apache Airlines air taxi flight, operating as Flight 33, departed Tucson International Airport for Phoenix, Arizona. The aircraft, a De Havilland Dove Model 104-7AXC (Carstedt CJ600A Conversion), registration N4922V, carried two crew members and ten passengers. During the flight, witnesses near Coolidge, Arizona, observed the plane traveling northwest. These observers noted loud engine noises that abruptly stopped, followed by the aircraft entering a steep descent of approximately 45 to 50 degrees.
No smoke or fire was visible from the aircraft during its descent, and no structural separation was seen by onlookers. The wreckage was located in a plowed field, where investigators found two separate impact craters. One crater contained the fuselage and left wing, while a second crater, situated about 35 feet away, held the right engine and portions of the right wing. The debris field showed significant fragmentation, particularly on the right side of the airframe. The accident resulted in 12 fatalities.
Findings
Post-accident investigations focused on the structural integrity of the aircraft. While witnesses reported unusual engine sounds, mechanical examinations of both engines and fuel systems showed no evidence of malfunction or failure prior to the crash. Both propellers were found in the feathered position, and no pre-existing damage was identified on the engine mounts.
The investigation concluded that the primary cause was the structural failure and separation of the right wing during flight. This failure originated from a fatigue fracture in the lower main root joint fitting. The fracture spread from an area affected by corrosion and fretting damage, which was attributed to underlying design deficiencies. Furthermore, inadequate oversight of the supplemental type certification and modification programs meant these specific inspection and design requirements were not properly maintained.