Black Box Tells Its Secrets

The "black box" in an aircraft is actually orange in color with two white stripes painted on its surface.

"It is like a shock-proof, heat-proof tape recorder," says Mr. Hellyer, Cathay Airlines technical services superintendent of aircraft electronics. "About half the size of a home video recorder, it is bright orange in color so that, in the event of a crash, it can be more easily found. Inside its one-centimeter-thick steel case is a layer of waxy insulating material, three centimeters thick, for extra fire-resistance and to reduce the shock of impact. Inside this is the motor, electronics and 160 meters of magnetic tape which records about 50 aspects of the aircraft's operation over the previous 25 hours.

"It weighs 10 kilograms and can withstand heat of 1200 ° C over half its surface area for 30 minutes as well as the weight of very heavy, sharpened spikes being dropped on it. It is almost indestructible. However, in the case of the EL AL aircraft which crashed into a tower block in Amsterdam only minutes after take-off, the device was so badly damaged by the resulting fire and explosion of the plane's full petrol tanks that the tape could not be played back.

"The black box is also fitted with an underwater beacon which gives off ultrasonic signals when an aircraft crashes into the sea and this signal helps in the search for the location of the crash. In 1974 a TWA Boeing 707 exploded in mid-air above the Ionian Sea near Greece. When the wreckage was eventually found a month later, the black box was found lying on the ocean bed 3km below the sea surface, still signaling," he continued.

The black box was made compulsory for all aircraft in the late 1950's and is located near the tail of the airplane. It is the safest area as the tail is usually found to be the least damaged after a crash. Next to it is another armored box, the cockpit voice recorder which records everything picked up by a microphone in the cockpit on a tape loop 30 minutes long. The two boxes look very similar and sometimes even rescuers mistake one for the other.

At the front is another unit, not designed to withstand a crash. Called the brains of the system, this flight data acquisition unit collects data from all over the aircraft and compresses it into a single stream of digital data to be sent to the crash-proof recorder.

After a crash and when the black box is found, the accident investigators play the tape and present their evidence. "The pilot could have been careless or the manufacturer could have been at fault or a bomb could have been placed on board," says Mr. Hellyer. "Whatever the cause, the black box can point the finger of blame."

"Apart from that, the box is also used on a day-to-day basis to help locate any problems in maintenance, check each engine's performance and in other ways. This data will ensure even more safety for passengers and crew," Mr. Hellyer concluded.