The CFM56 first ran in 1974 . In April 1979 , the joint venture had not received a single order in five years and was two weeks away from being dissolved . The program was saved when Delta Air Lines , United Airlines , and Flying Tigers chose the CFM56 to re-engine their DC-8s and shortly thereafter it was chosen to re-engine the KC-135 Stratotanker fleet of the U.S. Air Force – still its biggest customer . The first engines entered service in 1982 . Several fan blade failure incidents were experienced during the CFM56 's early service , including one failure that was a cause of the Kegworth air disaster , and some engine variants experienced problems caused by flight through rain and hail . Both these issues were resolved with engine modifications
Kegworth air disaster
Kegworth air disaster
CFM International CFM56