Large commercial aircraft and some smaller aircraft must be equipped with a cockpit voice recorder and a flight data recorder. These devices are usually in the aircraft's tail section and are equipped with beacons to help locate planes.
Through a microphone on the overhead instrument panel in the cockpit, the cockpit voice recorder records radio transmissions, voices, automated warnings and other aircraft noises. From these sounds, investigators can determine times of events, engine revolutions per minute, system failures, speed and other parameters.
The flight data recorder monitors various flight operating conditions including altitude, airspeed and heading. Some devices can monitor more than a thousand parameters, ranging from flap position to whether the auto pilot is engaged. Investigators use this data to help visualize the final moments of a flight by creating computer animated video reconstructions.
Once the cockpit voice recorder and flight data recorder are located after an accident, data stored on the recorders is extracted and translated into an understandable format. This information helps investigators determine the probable cause of an accident.
