Clues only raise more questions about doomed EgyptAir flight

The Egyptian government has sent a submarine to the search area to try to retrieve the EgyptAir Flight 804's flight recorders or so-called black boxes, which could finally explain what went wrong when it mysteriously crashed in the Mediterranean Sea last week. The U.S. Navy found more than 100 pieces of debris over the weekend.

The first audio recording to be released from the plane's flight deck is a standard check in between the pilot and air traffic control over Zurich in Switzerland, reports CBS News correspondent Holly Williams.

"EgyptAir 804 contact Padova 1-2-0, decimal 7-2-5, good night," Air Traffic Control said.

"This is 0-7-2-5 Padova control. EgyptAir 804, thank you so much. Good day, er, good night," the pilot responded.

Around two and a half hours later, the plane began to move erratically and then plummeted, disappearing off radar screens and plunging into the water.

The search area is around 180 miles north of the Egyptian coastline, where the American search team spotted wreckage from the plane and the Egyptian military retrieved debris from the crash.

A U.S. intelligence official told us the plane's flight recorders have been approximately located via the electronic pings emitted by their beacon. But there's been no official confirmation of that from Egypt, and retrieving the black boxes in water up to 10,000 feet deep will be difficult.

Data published by an aviation industry website appears to show automatic transmissions from the plane in the minutes before it crashed, indicating there was smoke onboard, though experts say the smoke alarms could also have been triggered by a sudden loss of pressure.

"It means that something big has happened on the aircraft. Multiple failures mean they are in serious trouble and that is not a normal situation," said Alastair Rosenschein, a former pilot with British Airways. "Could be caused by an explosion, could be caused by fire."

No possible cause of this crash has been ruled out including terrorism, though U.S. investigators say at this point there have been no credible claims of responsibility.