Complex sentence: Military jets that had been dispatched to intercept Schrenker's plane, discovered its door open and cockpit empty--and followed the plane until it crashed just north of Milton, Florida at about 9:20pm.
Split into simpler sentences: Military jets that had been dispatched to intercept Schrenker's plane discovered it in flight, with its door open and cockpit empty. They followed the plane until it crashed just north of Milton, Florida at about 9:20pm.