Using computer models of currents and wind direction, searchers then scoured a vast area to the northwest of the plane's last known location without luck.

In the end, the wreckage was found last month much closer to the plane's last known location following three failed expeditions at a cost of more than 25m.

If the unit stops transmitting upon impact, the historical transmissions will give the last known location of the aircraft, its speed, direction and altitude.

Animals use it to estimate their current location based on their movements from their last known location.