Planes and vessels from Egypt and five other countries - Greece, Britain, France, the United States and Cyprus - continued searching a wide area of the eastern Mediterranean on Saturday, a day after the Egyptian military found debris from the passenger jet in the sea 180 miles north of the Egyptian port city of Alexandria. The waters in the area are 8,000 to 10,000 feet deep, and the pings from the black boxes can be detected up to a depth of 20,000 feet.

Once found, the black boxes will determine the reason for the crash. On Friday, the widely accepted theory that a terrorist attack was responsible for the crash was put in question when new information was transmitted from the flight indicating that smoke was detected on the plane before it crashed. According to the sources, the information indicates smoke was coming from one of the engines. The data was transmitted through the Aircraft Communications Addressing and Reporting System, which sends snapshots of engine performance throughout the flight.

Adding to the confusion, however, is the insistence of Egyptian authorities who believe terrorism is a more likely explanation than equipment failure, and some aviation experts have said the erratic flight suggests a bomb blast or a struggle in the cockpit. But so far no hard evidence has emerged.