A submarine has been deployed to search for the missing flight recorders – or 'black box' – from the EgyptAir plane that crashed in the Mediterranean on Thursday. The reason behind the plane's erratic movement and sudden descent into the sea are still unknown though rumours are circling around possible mechanical failure or terrorist attack.

The sub is a new stage in the search, which is against the clock – after 30 days the batteries on the flight recorders will go flat and the location signal they send out will stop sending out location signals, making them much harder to find. Any help is useful to navigate the mountainous seabed which can go two miles deep.

The last three minutes of the jet was revealed in automatic messages from the plane's aircraft communications addressing and reporting system (ARCAS). The first message showed that smoke had been detected in a lavatory near the front of the plane and that two windows in the cockpit had problems.

A minute later alarms went off in the avionics bay as smoke was detected there – the avionics bay is where the electronic and computing systems are stored, it is below the cockpit. Another minute after that an alert suggests that a cockpit window was open. The final message showed that the flight control unit and spoiler-elevator computer had gone down.

The ARCAS system automatically sends alerts to the airline headquarters.

Greece said that the EgyptAir flight made two sharp turns before rapidly descending into the sea. EgyptAir's chairman, Safwat Moslem, said on Egyptian TV that the search zone radius was 40 miles – around 5,000 miles sq, and it that it could grow.

Though debris including luggage and human remains has been found, the plane's main body has yet to be recovered. The plane's body will contain two 'black box' flight recorders which record data from the flight and cockpit transmissions.