LITTLE ROCK, Ark. — Investigators found no evidence of mechanical failure to explain why a pilot lost control of a small plane that nosedived into an Arkansas ridge, killing the Oklahoma State women's basketball coach and three others, according to a federal report.

An examination of the wreckage revealed no instrument failure and no anomalies in the engine or airframe before the Piper PA-28-180 went down near Perryville, Ark., on Nov. 17, 2011, National Transportation Safety Board said in a report dated Wednesday.

Oklahoma State coach Kurt Budke, 50, and assistant coach Miranda Serna, 36, were killed in the crash, along with the 82-year-old pilot, Olin Branstetter, and Branstetter's 79-year-old wife, Paula. They were flying from Stillwater, Okla., to North Little Rock to scout two prospective high school recruits.

The NTSB concluded that the probable cause of the crash was Branstetter's loss of control of the aircraft, but investigators found no evidence that the pilot had a medical issue that may have contributed to the accident. The board early on ruled out weather as a factor.

"The reason for the pilot's loss of control could not be determined," the report concluded.

According to Federal Aviation Administration records, Branstetter had passed a medical examination, was certified to be a commercial pilot and was flight-instrument rated.

The Associated Press emailed NTSB investigator Jason Aguilera seeking comment Thursday.

The report said the aircraft was flying at 7,000 feet when it turned right and started to descend, soon vanishing from radar. Branstetter didn't contact air traffic controllers prior to hitting the ridge near Perryville, about 45 miles northwest of Little Rock. The crash occurred at 4:10 p.m.

"Witnesses who were near the accident site reported seeing the airplane flying at a low altitude and making turns. They then observed the airplane enter a steep nose-low attitude prior to descending toward the terrain," the report states.

Authorities said hunters in the Winona Wildlife Management Area called 911 to report that they had seen a plane in trouble.

Branstetter — a former state senator, an OSU graduate and supporter of its athletic programs — was piloting a "donor flight" so the coaches could watch high school games. The plane was registered to him and he was also certified to be a commercial pilot.

The crash was the second major tragedy for the OSU sports program in about a decade. In January 2001, 10 men affiliated with the university's men's basketball team died in a plane crash as they headed home after a game in Colorado. The NTSB attributed the crash to a power loss aboard the aircraft and said the pilot suffered disorientation.

The university introduced rules after that crash to prevent players from traveling on single-engine planes such as the one that went down in Arkansas. Since the most recent accident, OSU has expanded the rule to include coaches and staff, and pilots and aircraft must be reviewed by an aviation consultant.