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What is a black box and how does it work?

When a plane crashes, you need to retrieve the black box in order to establish the causes of the accident. A black box flight recorder is a heavily protected recording device that records all relevant flight data and the conversations in the cockpit. Every airplane must have two of these devices on board.
A black box must be virtually indestructible. So they are tested to see if they can withstand:

  • an impact with a concrete wall at 750 kilometers per hour (about 466 miles/hour)
  • a static load of 2.25 tons for at least five minutes
  • water pressure found in depths of up to 6,000 meters (about 19,700 feet)
  • a maximum temperature 1,100 degrees Celsius (2,012 Fahrenheit) for one hour

It may not always be clear where an aircraft has gone down, especially if it happens over remote stretches of ocean. In order to be easier to find at sea, all black boxes have underwater locator beacons which transmit a signal upon contact with water. One problem though is that the radius for the signal is about two kilometers (1.2 miles).
The black box records everything but the discussions can only be evaluated in order to clarify accidents or malfunctions and the recordings are overwritten after a maximum of 120 minutes
Did you know that the black box has never actually been black? The color must be bright orange!