Rudy Kapustin, a former government plane crash investigator who works as a consultant in Maryland, said the voice recorder on one plane downed by a bomb outside this country recorded the sound of the explosion. We were able to pick up the thud. In another case, Furman said, the speed of the recorders started to slow down, indicating that the plane was running on battery power. Furman said that in a 1985 Delta crash near Dallas, the cockpit conversation helped investigators determine that the cause was windshear. It was information the air traffic controllers never had been told, Furman said.
Nobody takes the time to communicate to the tower while it's going on.