 The NTSB concluded that DAL 379 was not actually "clear of the runway" because its jet exhaust continued to pose a hazard to aircraft attempting to use runway 27L.The jet blast from DAL 379 caused a compressor stall in Flight 159's number four engine.The compressor stall caused a loud noise heard by the pilots, and the jet blast caused a movement of the Boeing 707's flight controls during the takeoff.