The CFM56 first ran in 1974. By 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 Boeing 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.