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Why is it that black boxes don't float?

From what I gather the answer is:

So they will not float away from a water crash site. The ping can be heard underwater with sonar. Finding the ping, finds the site.

But why not have two black boxes one that floats and one that stays with the aircraft?

That way if a plane is lost at sea, if we find the black box floating, we could use the data to find the other black box and the crash site. Plus the benefits of having a redundancy are enormous.

Arian Faurtosh
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    for the record you are counting the FDR and CVR as one set of boxes right? – ratchet freak Mar 24 '14 at 20:22
  • @ratchetfreak yes both of them, but I believe it's a CVR – Arian Faurtosh Mar 24 '14 at 20:23
  • It is true that most CVRs and FDRs are technologically backward. The industry is starting to question why they are fitted at all. The technology exists to transmit the key data points (you don't need it all) to external storage, by data link when available, by satellite when not. I expect (OK, guess) that the next generation of aircraft will bring data logging into the 21st century. It's already done to an extent for the engines. It's only time before the rest catches up. – Simon Mar 24 '14 at 22:42

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The added weight, space, and complexity of a second recorder have to be taken into account, and all are very important for an airplane.

If you are just interested in location, then there could just be a simple beacon designed to float. Although less, this will still have the above costs. And you have to design something light enough to float, sturdy enough to survive an extremely violent crash, yet still be a functional electronic device.

Considering that the situation of a lost aircraft at sea is fairly rare, it is questionable whether the benefits justify the costs.

fooot
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    Although circumstances of a lost aircraft at sea are fairly rare, the cost of searching for one is enormous... The cost to find air france was about $50 million, and I am sure flight 370 will be much greater... It might be fairly rare, but it's expensive. – Arian Faurtosh Mar 24 '14 at 20:30
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    True, the search is very expensive. But designing a beacon, certifying it, installing it on the fleet, and flying it around and maintaining it will add up very quickly. And unless it is somehow mandated, it will be just like the services we have available today that airlines don't want to pay for. – fooot Mar 24 '14 at 20:35
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    How much would it cost to have both black boxes record both flight data and the cockpit audio, rather than having one for each? Having separate boxes for data and audio may be better than having one for both, in that it maximizes the likelihood of recovering at least something, but having the boxes be fully-redundant would seem like a cheap way of maximizing the likelihood of recovering the most interesting information. – supercat Jan 19 '15 at 17:07