airliner. 66 people are on that flight from cairo. >> distinct sounds from the floor of the mediterranean sea could lead to the first substantial clues to what happened to egyptair flight 804. so far searchers have only retrieved scattered aircraft debris and human remains. not the main body of the plane. but a french naval ship with three underwater listening devices detected sounds investigators say belonged to the cockpit voice recorder or flight data recorder of the airbus 320. that's a sample of what signals from black boxes sound like. inside those boxes investigators hope to find answers to what brought down the plane. >> these are the four different channels from a cockpit voice recorder. first officers and one if there's a third crew member.