The
Black box that the
press refers to on a plane. There are more than 100
black boxes on a plane, but most are only used for minor maintenance, and the most important one is the Flight Recorder.
Actually, it's bright orange, so it can be spotted by salvage crews and scuba divers. And it's waterproof. It's placed in the back of the plane, by the tail, which usually stays more intact than the front. It's very heavy, surrounded by reinforced crash-resistant housing. The actual recorder weighs a few ounces.
In the event of a plane crash, the Flight recorder is used to reconstruct the accident, along with the Cockpit Voice recorder (CVR). The Flight recorder contains logs of the instrumentation, and any lights on the cockpit's dashboard, as well as airspeed, altitude, etc.
Even though planes are required by the FAA and in Europe, the JAA, to have a working flight recorder, in truth, many are faulty. In a study, random Flight Recorders were taken out of service and tested, and few of them were 100% functional. Some faults include faulty circuits, blown fuses, and other failures.
Although not required, a QAR is also used to take note of faults after a trip, for maintenance.