Delta Air Lines Flight 9570 crashed on 30 May 1972 at the Greater Southwest International Airport in Fort Worth, Texas while conducting a training flight. The aircraft, a McDonnell DouglasDC-9-14, began to oscillate about the roll axis after crossing the runway threshold during a landing approach, then rolled rapidly to the right and struck the runway with the right wing low. This flight's crash has been attributed to wake turbulence behind a McDonnell Douglas DC-10 that made a touch-and-go landing ahead of it. The plane's occupants consisted of three pilots and an FAA inspector, all of whom were killed in the crash and subsequent fire. The resulting investigation prompted changes to the minimum distance that aircraft must keep when following "heavy" aircraft.