The two occupants of a small plane that had crashed in a semi-rural area of Ventura County were identified Friday.

Michael Dwain Boolen, 59, and Harry Allen Bell, 89, were killed when the single-engine Ultralight Stingsport in which they were flying crashed to the ground Thursday. Both were pilots and flight instructors.

Boolen was from Pacoima, while Bell was from Newhall, according to the Ventura County Medical Examiner's Office, which released the names Friday.

The Federal Aviation Administration said the crash came amid "unknown circumstances," and that the agency and the National Traffic Safety Board would investigate.

The crash site, shown below at right, was about 2 miles east of the unincorporated mountain town of Piru on what appeared to be the grounds a ranch house. The plane was in a dirt area surrounded by an orchard.

Boolen and Bell were dead when Ventura County Fire Department first responders arrived on scene, authorities said.

According to his website, Boolen was a professional pilot and flight instructor with more than four decades of aviation experience. He was based at Whiteman Airport in Pacoima, where he did electrical engineering consulting for aviators.

A small memorial had been set up at the airport, with a burning candle and red roses.

A woman who identified herself as the owner of Rocky's V airport restaurant, next door to Boolen's flight training office, said Boolen was "a very upbeat, positive, fun-loving person" who "loved to fly."

Boolen and Bell were traveling in a plane built in 2007 that was registered to Bell, whose address was listed as Bullhead City, Ariz., according to FAA records.

It was not known which man was the plane's pilot, Sgt. Eric Buschow of the Ventura County Sheriff's Department said.

Like Boolen, Bell was a licensed pilot and certified flight instructor, Buschow said.