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After several delays, the plane's black boxes have now arrived in the UK after the rebels handed them to investigators.

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And what happens next here is experts will analyze the information contained on those devices, but information learned from that could take weeks.

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CNN's Rachel Crane takes a look at why black boxes are so crucia to an investigation after a plane goes down.

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Following a plane crash, the search for survivors always comes first.

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But just as important is the search for answers -- the why and the how.

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Often, those answers are found in the black box.

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Since the '60s, all commercial airplanes have been required to have one on board.

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Now, the name is a little misleading, because they're actually orange.

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And when we're talking about a black box, we're talking about two different boxes --

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one being the cockpit voice recorder, the other being the flight data recorder.

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Together they weigh anywhere between 20 to 30 pounds and they have to be crash-proof.

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Black boxes can survive just about anything --

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temperatures up to 2000 degrees Fahrenheit for an hour, forces that are 3,400 g's; now, it's 3,400 times the force of gravity.

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They're waterproof and they can save recorded data for two years. And it's a lot of data.

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The cockpit voice recorder records the crew's conversation and background noise.

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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.

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When these sounds are cross-referenced with ground control conversations, they can even help searchers locate a crash site.

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Then there's the flight data recorder.

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It gathers 25 hours of technical data from airplane sensors, recording several thousand discrete pieces of information --

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data about the air speed, altitude, pitch, acceleration, roll, fuel, and the list goes on and on.

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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.

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Both black box components are outfitted with underwater locater beacons, which self-activate the moment they come into contact with water.

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They send pings once per second to signal their location

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and can transmit data from as deep as 20,000 feet for up to 30 days, when their batteries then run out.

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But on land, there's no such pinging to help guide the search.

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Investigators have to sift through the wreckage until they find it.