Separation
For instance: An aircraft has just taken off from an airport. The aircraft is on a routine nightly flight on an IFR flight plan. The aircraft is still on departure control, 8.1 DME from the VOR, which is on the field, on an assigned heading and altitude and has just intercepted a Victor airway. Suddenly something with a lot of force hits the aircraft and it crashes at that location. I know this is vague but this is a very quick summary of facts.