Malaysia Airlines MH370: the black box explained

What is Black box?
Aviation experts warned in March last year that the crucial moments of doomed Malaysia Airlines flight MH370 may never be discovered, as the 'black box’ which records details of the flight may have overwritten key data.
A 'black box' actually consists of two boxes – a cockpit voice recorder and a data recorder. The flight data recorder records a stream of flight information, while the cockpit voice recorder stores conversations and other noises made in the cockpit.
Each of the boxes is about the size of a shoe box and weighs around 10kg. They are made out of aluminium, and are designed to withstand massive impact, fire or high pressure. Although the original flight recorders were painted black, the colour was changed to orange to make them easier to find by investigators.
The Boeing 777 aircraft disappeared on March 8 last year, carrying 239 passengers and crew shortly after taking off from the Malaysian capital of Kuala Lumpur, bound for Beijing. In January, Malaysia's government released a statement formally declaring the crash an accident.
The black box on Malaysia Airlines flight MH370 is made by US firm Honeywell Aerospace. It is programmed to record cockpit communication on a two hour loop and delete all but the final two hours.

This is because it is normally the last section of a flight that determines the cause of a crash. In the case of Air France flight 447, for example, the cockpit voice recorder provided a valuable insight for investigators into the confusion that overcame the pilots.
In the case of MH370, however, it is thought that the crucial moment for understanding the flight revolves around the period during which its communications systems were disabled and it took a sharp turn westward before flying silently for about seven hours.
Although the flight data will have survived, the discussion in the cockpit immediately after the flight lost contact with air traffic control will have been overwritten, unless power to the recorder was lost at the same time.
The black box sends out a ping, activated by immersion in water, that can be picked up by a microphone and a signal analyser from about a mile away.
However, the battery of the pinger on MH370 only lasts for 30 days and the mystery may never be solved as the black box has still not been found.
The depth of the area of ocean that investigators were searching ranged from 1,150m (3,770ft) to 7,000m (23,000ft). The detector could have picked up the black box pinger down to a depth of about 6,100m (20,000ft).