KAL 7's ''black box,'' the prize that United States and Soviet salvage teams race to recover from the Sea of Japan, isn't black at all. It's high-visibility yellow. And it is, in fact, two boxes. One contains a taped record of what the cockpit crew said during their last half-hour. The other holds the flight data recorder, which measures such things as speed, heading, altitude, and engine power.
Mounted near the tail of a plane, an area that often stays intact in a crash, the boxes are built as strong as wall safes. Data are recorded, for instance, on metallic tape that is just about fireproof. Aviation industry sources have little doubt that the recorders in Korean Air Lines Flight 7 are still intact.
''In 17 years with a major airline,'' says one source, ''I've investigated 10 crashes, from a plane going head-on into a mountain to one sinking underwater. The boxes always survive.''
The recorders are equipped with a sonar beeper to aid in underwater retrieval. This electronic cry for help, powered by a 30-day battery, is what US vessels may have heard on Monday, before bad weather forced officials to suspend salvage operations. As of this writing, the box had not been retrieved.
US airliners have been required to carry black boxes since ''the start of the jet age, the early '60s,'' says Fred Farrar, a spokesman for the Federal Aviation Administration. Most countries, including Korea, have similar requirements.
''The reason they're needed, of course, is that they're invaluable aids in investigating an accident,'' Mr. Farrar says.
KAL 7's cockpit voice recorder may yield the definitive answer as to whether the plane's crew knew they were over Soviet territory and in danger from Soviet fighters.
The flight data recorder would help investigators reconstruct what happened after the plane was shot. Jack Gamble, a Boeing spokesman, says that ''the data recorder monitors systems, such as engines, and changes in systems'' - so it could establish where KAL 7 was damaged by Soviet missiles. Altitude and heading information would reveal the jet's path as it plunged into the sea.