Black Box

black box is a recording machine carried by commercial and military aircraft and aboard the Space Shuttle. Designed to survive a crash, it is used to find out how an acci­dent occurred. Airplane crashes are very rare, but when a fatal accident does happen, it is important to find the cause. Knowing why one aircraft crashed may help to prevent other accidents.

After an accident, a team of investi­gators search through the wreckage, looking for clues. They also look for the piece of equipment referred to as the

THE FIRST BLACK BOX

The development of the black box flight recorder began in Australia in the 1950s. There had been a series of air crashes with no witnesses and no survivors. It was very difficult to find out what caused them. Dr. David Warren at the Aeronautical Research Laboratories of Australia wondered if a plane could be fitted with a recorder to give investigators infor­mation about a crash. His work resulted in the first flight data recorder in 1958. The first black boxes used magnetic tape to record and store information-today’s flight recorders use computer chips.

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black box. In fact, black boxes are not black-they are bright orange-and there are usually two of them.

The flight data recorder, one of the two black boxes, is the size of a large shoebox. To survive a crash, the box is made to withstand a force of 3,400 times the force of gravity for 6.5 milliseconds. (A millisecond is one-thousandth of a second.) It also withstands fire and being submerged in liquid.

The flight data recorder records hun­dreds of pieces of information about an aircraft. The data includes the aircraft’s speed, height, and direction. The device also records the positions of controls, the positions of the rudder and other control surfaces, and the engine speed.

The other black box is the cockpit voice recorder. It records sounds picked up by microphones in the cockpit. The pilots’ voices are recorded on one micro­phone. Another microphone in the cock­pit roof records the sounds of alarms, clicks of switches, and other background noises. At any moment, the box has retained the last thirty minutes to two hours of sound as a recording that can be retrieved if a plane crashes.

The information from both boxes is stored in computer chips. The chips are inside an extremely tough package called the crash survivable memory unit. The unit’s case is made of stainless steel or titanium. It is lined with fireproof insulation. To test the case’s toughness, the unit is fired out of a cannon and burned in a fire at 2000°F (1093°C) for an hour.

Some versions of the black box contain the flight data recorder and voice recorder in one unit. Whether they are combined

or separate, black boxes are usually installed in the plane’s tail, where they are most likely to survive. They may be thrown out of a plane by the impact of a crash, so they are designed to be easy to find. Apart from their bright color, they are fitted with a locator beacon that switches on automatically if the recorder lands in water. It emits an ultrasound pulse every second for a month. Divers or underwater craft can use the signal to locate the recorder. When a black box is found, the information in its memory can be downloaded and studied.

In the United States, black boxes are taken to the National Transportation Safety Board for expert analysis. Investigators include safety officials and representatives of the aircraft manufac­turer and operating airline. Together, these people try to piece together what happened in the last moments of a flight. Recorded conversations between
pilots can give clues, even if the pilots themselves did not know the cause of their problem. The flight data recorder offers minute detail of what the airplane was doing at any given second.