In order to locate an aircraft in flight, there is actually a transponder located inside a smallbox like this one here. Situated on the cockpit's central console, it sends a signal to the plane's control centre, on which it depends. These data indicate the aircraft on radar screens, indicating not only its altitude, position and speed, but also any malfunctions or changes of direction.
In the case of flight MH370, this transponder stopped working two hours after take-off, however, what is not known, is whether it was due to a breakdown, failure, a zone not covered by the system or even a deliberate act? It's too early to tell, but this transponder can in fact be manually disabled and does not work in some areas. Without the transponder, the primary ground-based radars, however, can locate an aircraft, although less accurately, and as long as it is less than 300 km (190 miles) away.
A plane is also tracked by the ACARS (Aircraft Communications Addressing and Reporting System). In fact certain aircraft systems automatically send reports directly to the maintenance centre for example, allowing any possible faults occurring during the flight to be repaired from the ground.
According to the US investigators, as part of its maintenance programme, Rolls Royce, the manufacturer of the Trent 800 engines that power the aircraft, would also have received messages for four hours after losing contact with air traffic control; information denied by the Malaysian authorities, and which, when we contacted them, remained unconfirmed by the engine manufacturer.
In addition to the ACARS, CPDLC (Controller-pilot data link communications), there is a system that allows written exchanges between pilots and controllers. This radio link is used to communicate orally; but here again, the aircraft stopped all communication, written and oral, two hours after the start of the flight – was this a technical failure or a deliberate decision of the pilots?
Finally, in the event of a crash, and even an in-flight explosion, the black boxes on board, together with the automatically triggered distress beacons should be transmitting signals indicating the aircraft's location. Unless the 777 is too far away from the area of current research, it's difficult to understand why no signals are being picked up from the plane - seven days after its disappearance. Many gray areas is still surround the disappearence of flight MH370.