We may only solve the mystery of flight MH370 when its black box is recovered. What is a "black box"?

More than a week after Malaysia Airlines flight 370 with 239 people on board went missing, search parties are still on the lookout. With the Aircraft and Communications Addressing and Reporting System (ACARS) being disabled just before the plane reached Malaysia’s east coast and the transponder (transmitter responder) being switched off shortly after that, satellite data based on the plane’s last communication has only been able to provide for two wide possible corridors. As the world’s air traffic control network is still almost entirely radar-based, the mystery might only be solved when the black box flight recorders are recovered.

For decades after the aviation industry came into existence, crashes and disappearances could hardly ever be explained. While the idea and the necessary technology to build flight recorders to store data about the aircraft while in flight existed, they were still not in place even in the 1950s.

David Warren, a researcher at the Aeronautical Research Laboratories in Melbourne, Australia, was involved in the accident investigation of the world’s first jet-powered commercial aircraft, the de Havilland Comet. Warren believed that if he could yoke together recorded voices of the pilots along with readings of the instruments, they could glean vital information. Using the black box, which he called a “Flight Memory Unit”, he was sure that they could determine the cause of a crash, and hence, help prevent further instances of the same.

The first prototypes, which could store up to four hours of information, were ready by 1957. Even though Warren expected them to be instantly popular, the device was rejected by Australia on grounds of privacy issues.

British officials gave Warren the go-ahead and he soon began producing these for airlines across the globe. Following a 1960 crash in Queensland, Australia became the first country to make the black box mandatory on all commercial airlines.

Black boxes — which, interestingly, are not black in colour but orange — these days go through severe testing to ensure that they can survive severe aircraft accidents. Ejected from the rear of the aircraft at the moment of an accident, these can endure a 3400-g (1 G is the force of Earth's gravity) crash impact, survive fire and piercing and also withstand the pressure of being submerged in the ocean up to a depth of 20,000 feet.

The main components of a black box are the Flight Data Recorder (FDR), Cockpit Voice Recorder (CVR) and the Underwater Locator Beacon (ULB).

While the FDR records flight conditions like altitude, airspeed, accelerations, direction the plane is heading and time, the CVR stores sounds within the cockpit, including what the crew says. This information, which used to be stored using steel foils, is now recorded using solid-state memory, which can be downloaded instantly. The ULB, which is activated as soon as it comes in contact with water, transmits ultrasonic signals from as deep as 14,000 feet, enabling it to be located. However, these signals have a limited range and therefore will be detected by the search crews only if they are close to the crash site. In the case of Air France flight 447, which crashed into mid Atlantic in June 2009, the black box was retrieved after nearly two years. Also, no form of GPS location transmitter is currently fitted with these black boxes.

Plans to replace radar with a new system based on GPS positioning as the primary method of surveillance has gather momentum with air traffic controllers. The coverage of this system, Automatic Dependant Surveillance-Broadcast (ADS-B), would also however not extend over the oceans, as is the case with radar. The mystery of flight MH370 has brought back the debate over improving mid-air tracking.

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