Divers to Search for EgyptAir Black Boxes

They call them “black boxes.” Actually, they’re painted orange, because that makes them easier to find.

The two recording devices, each about the size of a rural mailbox, often provide vital information for investigators attempting to determine the circumstances and cause of an airplane crash like the one that claimed 217 lives off Nantucket Island on Sunday.

The bad weather plaguing the investigation of EgyptAir Flight 990 cleared enough Thursday that the Navy salvage ship Grapple and its divers could sail for the crash site to begin searching for the Boeing 767’s recorders.

The Grapple was expected to reach the site, 60 miles off the Massachusetts island of Nantucket, this morning, Navy spokesman David Sanders said. It wasn’t known when the divers could begin their work.

Rough seas and high winds have kept divers away from the crash site since Tuesday.

Because they are so important, cockpit voice recorders and flight data recorders are placed in the tails of modern jetliners, where they stand the best chance of surviving an accident.

Steel cases and cushioning help protect them from the impact of a crash. Watertight compartments help preserve them in the event of immersion.

National Transportation Safety Board investigators hope all this protection works, because the EgyptAir jetliner hit the ocean extremely hard--apparently at close to the speed of sound--and the recorders have been lying on the ocean floor at a depth of more than 250 feet.

However, even when the protective systems have failed, NTSB lab technicians have shown remarkable perseverance and ingenuity in recovering useful information from recorders that appeared to have been damaged beyond hope.

Locater transmitters triggered by the impact of Sunday’s crash have been broadcasting audible “pings” from the recorders. The Navy has rigged electronic search equipment on the Grapple, a ship that figured heavily in recovery operations after the crash of TWA Flight 800 off the coast of Long Island in 1996.

Once the recorders are recovered, lab technicians will get a chance to unlock whatever secrets are stored in the black boxes--so named because of their aura of mystery and the fact that, in the old days, some of them were painted black.

A cockpit voice recorder uses a microphone to pick up all the sounds heard on the flight deck--conversations of the pilots, aural alarms, the sounds of controls being moved and switches being thrown and even the noise of the engines. In addition, a link to the plane’s radios picks up all conversation between the cockpit crew and air traffic controllers.

Investigators have found that all these sounds can be useful in figuring out what happened--and what didn’t happen--before a plane crashed. A vital procedure inadvertently overlooked during a verbal rundown through a preflight check list can be as important as a pilot shouting out that a control system has failed.

Earlier aircraft used a loop of tape to record these sounds. On the Boeing 767 that crashed Sunday, the sounds were recorded digitally. Either system retains only the last 30 minutes of sounds in the cockpit, erasing earlier recordings.

The flight data recorder logs information on technical aspects of the flight. The devices have varying capacities and are usually tailored to the requests of individual airlines.

The flight recorder on the EgyptAir jetliner was designed to amass 55 different types of information--including altitude, airspeed, rate of climb or descent, the direction in which the plane was flying, any maneuvers it was making, the setting of various controls and the position of the control surfaces on the wings and tail, the rate of fuel consumption, thrust-reverser settings, throttle settings and the amount of power actually being produced by the engines. Again, all this information was logged digitally.

After being recovered, the recorders will be shipped to the NTSB laboratories in Washington, where a cadre of specially trained experts will extract the information.

If the recorders are in good shape, the task will be relatively simple. Given the high-speed impact of the crash, however, that seems unlikely.

But the NTSB lab technicians are resourceful.

If the conversations recorded in the cockpit are indistinct or broken up, language experts--in this case, linguists familiar with Arabic--can be brought in to help decipher what was said.

Friends familiar with the pilots’ voices can listen in to help determine who said what. Computers can be used to unscramble words when two or more people are speaking at the same time. Pilots familiar with cockpit jargon and procedures sometimes can interpret apparently meaningless phrases and make informed guesses as to which switch was being thrown when a click is heard. Analyses of engine sounds can provide surprising amounts of information about how those engines were operating.

Even in instances where the electronic coding in the flight data recorder has seemed fatally garbled, electronics experts have been able to coax out at least a little useful information.

“It’s not easy,” an NTSB official said. “But these people are good at it.”