The U.S. Air Force has announced that 170 or more of it’s F-15 Eagle fleet will be going to the bone yard. Failure of a fuselage longeron has been sited as the primary cause of the crash of an F-15 last November. The grounding will affect four models of the U.S. fighter. The F-15E Strike Eagle is not included. 60% of the entire fleet has been returned to service.