All commercial airplanes are equipped with what is colloquially known as the Black Box, which is actually two separate electronic recording devices: the cockpit voice recorder (CVR) and the flight data recorder (FDR).

In the event of a crash, both are important in helping investigators reconstruct what happened before the crash, and what might have led to the accident. The recorders are painted bright orange or red to make them easier to find, but the original name Black Box stuck.

Australian scientist David Warren invented the Black Box in the 1950s, and in 1960, Australia was in fact the first country to make the Black Box mandatory on commercial aircraft. The US made them mandatory in 1967.

Memory boards

The FDR records the plane's operating functions, from altitude and airspeed to where the plane is headed, the fuel gauge and the auto-pilot. Data is stored on the recorder and can later be evaluated, making it vital in the investigation of any aviation accident. The recorders have to be able to withstand extrmeme impacts, are housed in steel casings and are essentially designed to be virtually indestructible.

The Airbus A320's FDR is expected to give crash investigation authorities a detailed readout of hundreds of parameters, including commands issued from the co-pilot's seat during the Düsseldorf-bound flight on March 24. Information will be matched with CVR recordings and information from ground radar.

Fatal course

The plane's CVR, which was found last week, is an independent device that records the crew's voices, interaction with air traffic control and other background sounds and noise. After evaluating the recording, investigators said they believed the 27-year-old co-pilot locked his captain out of the cockpit during the flight and deliberately plunged the plane into a French mountainside, killing all 150 passengers and crew.

Both the CVR and the FDR are also fitted with locator beacons that emit signals for 30 days before the battery runs out.

Critical flight date

In response to last year's disappearance of Malaysia Airlines Flight MH370 with 239 people aboard, the US National Transportation Board (NTSB) took the discussion on international standards for airline flight tracking a step further.

In a series of recommendations earlier this year to the Federal Aviation Administration (FAA), the NSTB re-emphasized "the need for cockpit image recorders on commercial airplanes" to help determine the causes of aviation accidents.