The National Transportation Safety Board says the pilot's loss of control caused a plane crash that killed him, his wife and two Oklahoma State University women's basketball coaches.
The crash happened on November 17, 2011 near Perryville, Arkansas. OSU women's basketball coach Kurt Budke and assistant women's basketball coach Miranda Serna died in the crash, along with pilot Olin Branstetter and his wife, Paula.
The Branstetters were long-time supporters of OSU.
The NTSB's Probable Cause report lists the cause as simply this: "The pilot's loss of control in flight."
It says the reason for the loss of control could not be determined.
The report says witnesses reported the plane flying low, descending and making several turns before impacting the ground.
According to the NTSB's Factual Report, released in January 2013, both Olin Branstetter and his wife, Paula, were experienced pilots but Mr. Branstetter was at the controls when the plane crashed.
The crash led Oklahoma State University to change its travel policy for employees and student athletes.