At the initial stages of an unfortunate major air accident's investigation, one of the first things to be sought after is the Black Box, or the aircraft's data recorders. The Black Box, which is actually orange, are actually two separate recorders. One is the Cockpit Voice Recorder, or the CVR. This records all the conversations and audible events taking place in the flight deck of the aircraft. The other is the Flight Data Recorder or FDR.
The FDR records hundreds of parameters of data, from the amount of deflection of the flight control surfaces (elevators, ailerons, and rudder) to the power setting of the engines, even down to the brake temperature on most modern jets. Since all these parameters of flight data can assist investigators get a picture of what was going on in the final minutes of a flight, it is no surprise Search and Rescue teams start to scour the crash site for these recorders as soon as they get on scene.
The first attempt at building a flight data recorder was in 1939 by two Frenchmen, Paul Beaudouin and Franois Hussenot. Their invention was nothing more than a mirror which reflected the pilot's instruments onto a very long photographic film, which essentially recorded basic parameters such as airspeed, altitude and heading. The major disadvantage with this system was that the film had to be replaced every number of odd hours.
The first true flight recorded was conceived by Dr. David Warren in the early 1960's. Dr. Warren developed effective means of recording parameters and cockpit audio, storing them into a case that could take high speed impacts and temperatures. Thus the first modern flight recorder came into existence.
Modern day recorders have to be up to standards set by the International Civil Aviation Organization. They have to be capable of surviving high acceleration forces (the minimum is 3400g's for about 6.5 milliseconds). They also have radio beacons that start transmitting their location after a crash, making recovery less difficult.
Although primarily for safety, flight data recorders are also being used by airlines to improve efficiency. Some airlines have fitted on their fleets with Quick Access Recorders. These can be accessed easily and can be used by the airline to determine if the engines on the aircraft are running inefficiently or even record things such as the quality of the runway surface. Another mundane usage of a Quick Access Recorder is to record toilet usage. By working out the average usage of toilet water, the airline can load their aircraft with less water, saving costs.
Flight Data Recorders improve safety, and allow investigators to figure out what exactly happened. They are therefor indispensable in their roles, and a major contributor to ensuring that commercial aviation is the safest way to travel.