The French accident investigation agency said Wednesday that it is not hopeful that the black box of the missing Air France airliner would be found.

"Black box" refers to both of the flight recorders called flight data recorder and cockpit voice recorder responsible for recording flight parameters and all communications in the cockpit of an aircraft in flight.

The investigators also said due to the complexity of the situation, they even had no exact idea of where the crash occurred and where the debris is, two days after the tragedy.

The crash is said to be one of the worst in the history with 228 passengers on board

A naval mission was launched after the debris was spotted off Brazil's coast, and ships heading to the zone are carrying two mini-submarines, the best hope of tracking down the boxes, which ought to emit a location signal.