CNN news 2016-05-24 加文本

CNN news 2016-05-24

Officials in the Mediterranean Sea have been searching for the wreckage of EgyptAir Flight 804. Early yesterday morning, it was traveling from Paris, France, to Cairo, Egypt. It had 66 passengers and crew aboard. When it was over the Mediterranean, at cruising altitude, the safest part of the flight, Greek officials say the plane swerved and then plunged and no one knows yet why.

Aviation authorities say it could have been some sort of technical failure or it could have been terrorism that brought the plane down. It had just passed from Greek air space to Egyptian air space when it dropped off radar and Egypt, France, Greece and the U.S. have all sent search vehicles to the crash site.

As the recovery mission unfolds and families wait for answers, officials are hoping the plane`s black box explains what happened.

(BEGIN VIDEOTAPE)

RACHEL CRANE, cnn CORRESPONDENT: Following a plane crash, the search for survivors always comes first, but just as important is the search for answers. The why and the how. Often those answers are found in the black box.

Since the `60s, all commercial airplanes have been required to have one onboard. Now, the name is a little misleading because they are actually orange. And when we`re talking about a black box, we`re talking about two different boxes --one being the cockpit voice recorder, the other being the flight data recorder.

Together, they weigh anywhere between 20 to 30 pounds, and they have to be crash proof. Black boxes can survive just about anything: temperatures up to 2,000 degrees Fahrenheit for an hour, forces that are 3400 Gs. Now that`s 3400 times the force of gravity. They are waterproof and they can save recorded data for two years and it`s a lot of data.

The cockpit voice recorder records the crew`s conversation and background noise. By listening to the ambient sounds in the cockpit before a crash, experts can determine if a stall took place, the RPMs of the engine, and the speed at which the plane was traveling. When these sounds are cross-referenced with ground control conversations, they can even help searchers locate a crash site.

Then, there`s the flight data recorder. It gathers 25 hours of technical data from airplane sensors, recording several thousand discreet pieces of information -- data about the air speed, altitude, pitch, acceleration, roll, fuel, and the list goes on and on.

But to make sense of the data, first you have to find it.

Not an easy thing to do when a plane crashes into the ocean.

Both black box components are outfitted with underwater locator beacons, which self-activate the moment they come into contact with water. They send pings once per second, to signal their location. And can transmit data from as deep as 20,000 feet for up to 30 days, when their batteries then run out.

But on land, there`s no such pinging to help guide the search. Investigators have to sift through the wreckage until they find it.

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