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Inside the Black Box



From left, Cushman holds a cockpit area microphone. The battered, bright orange case of a cockpit voice recorder recovered from a crashed airliner. The data recorders and other mechanisms of the CVR.

The first thing you notice about a "black box" is that it is neither black nor a box. Modern flight data and cockpit voice recorders tend to be flat plates, roughly the size of a shoebox, with cylindrical and squarish protuberances that contain the units' digital memory modules. To make them easy to spot at a crash scene (or, sometimes, well removed from the wreckage), they're painted bright orange. They're also equipped with radio beacons to make them easier to locate under water.

Typically attached to an airplane's rearmost bulkhead, where they are most likely to survive a crash, the recorders are designed to withstand intense heat and extreme G forces. Still, some arrive at the NTSB looking like defeated Robot Wars combatants. "When we started getting the older recorders back with [extensive] damage, we issued a recommendation to the FAA to change the law and increase the structural and heat requirements," Anna Cushman says. Most airlines will switch to newer, tougher digital units by 2005.

The data recorder tracks an airplane's altitude, airspeed and other vital flight parameters. The voice recorder stores four separate channels of audio. Three capture the feed from the pilot's and copilot's headsets and a cockpit area microphone usually mounted above the instrument panel. The fourth channel, originally designated for a flight engineer, now often records the announcements made over the plane's public address system. The microphones pick up engine noises, the sounds of mechanical devices (like landing gear deploying), warning signals, conversations with air traffic control or other pilots, automated weather briefings, and other noises that can provide clues about the causes of a crash or other incident.

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