What happened
A flight operated by the Phillips Aviation Department departed Bartlesville, Oklahoma, bound for Salt Lake City, Utah, carrying six passengers. The crew consisted of a pilot and a copilot-mechanic. During pre-departure procedures, the crew obtained IFR clearance via the company radio station. The aircraft, N 28366, an Aero Commander, departed at 0826 with a gross weight of 19,284 pounds, which was within allowable limits.
Approximately 14 minutes into the flight, the crew reported engine difficulties to Bartlesville Radio, noting that oil temperatures had exceeded 100 degrees. The copilot subsequently reported an inability to unfeather the propeller and requested runway condition information for Tulsa, Oklahoma. While the Bartlesville runway was covered in patches of snow and ice, the runways at Tulsa were clear. The crew indicated their intention to divert to Tulsa.
Following the last radio transmission, ground observers noted the aircraft traveling south of the airport at an estimated altitude of 3,000 feet. After flying east for several miles, the aircraft turned toward a southerly heading. Witnesses observed the plane enter a spin, plunging into the rolling terrain with a near-vertical nose-down angle. The impact resulted in an explosion and intense fire that destroyed much of the airframe. There were 6 fatalities.
Findings
Investigations into the accident revealed several key points regarding the mechanical state of the aircraft:
- The left engine experienced a bearing failure, which caused the propeller to feather.
- Although the right engine showed signs of high oil temperature, it did not exhibit evidence of malfunction.
- There were no visible defects found in the airframe or flight controls.
- The propeller and its feathering mechanism showed no signs of mechanical failure.
Loss of flying speed during single-engine flight was identified as the primary factor that led to the aircraft entering a spin.