OKLAHOMA CITY (AP) -- A collision between a crop duster and an Air Force jet in Tillman County earlier this year happened because the civilian pilot wasn't flying at the correct altitude, military investigators said. Carl Dierk Nash may have been trying to ascend in the AT-502B to the proper height when the crash occurred, according to a report released this week by the Air Force.

Nash, 43, owner of a flying service in Wheatley, Ark., died when his plane and a T-37B from Sheppard Air Force Base in Texas crashed near Hollister Jan. 18.

The pilots of both aircraft didn't see each other in time to avoid the collision, which happened at about 5,000 feet, Air Force investigators concluded. Visibility was limited because of a "hazy layer" of cloud between 4,500 and 6,000 feet, according to the Air Force. Nash was delivering the plane from a Texas factory to a customer in South Dakota. He had "extensive experience" as a pilot, according to the Air Force. The Air Force pilots, Capt. Christopher Otis and 2nd Lt. Roderick James, were returning from an area near Frederick where jets train daily.

Two ranch hands who helped the survivors said the crop duster burst into a fireball after the crash and the jet spiraled down as the pilots ejected.

The National Transportation Safety Board report may not be done for about a year, a spokesman said Tuesday.