A preliminary report on why a plane crashed in Lindsay, Okla. is expected to be released on Thursday.
William Jackson and Joe Grimes died last Saturday when Jackson's 2006 Cirrus SR 22 plane fell down near the town of Lindsay.
Air safety investigators said the plane was made of fiberglass and burned in the fire formed from the crash. National Transportation Safety Board officials are reviewing pilot log and maintenance books for clues on why the plane fell. Debris from the plane crash was also taken to Texas for examination.