It really bothers me that we can't find planes that weigh tons with black boxes (AFAIK) technology that's almost obsolete, on the other hand shark tags (AFAIK) work great for long time and we can monitor shark movement, depth, temperature, etc., all the time. So, why?
16$\begingroup$ Your question makes two unqualified assumptions - 1, that black boxes are often not found - in fact they are almost always are, and 2 - that shark tags are 100% reliable. I would suspect that some shark tags are lost, but this is not a big issue since many are tagged. $\endgroup$– ClydeMay 8, 2015 at 5:34
$\begingroup$ Yes, flight accidents are relatively rare and totally lost black boxes are more rare but it costs hundreds of lives and may be more if flight data that shows what had gone wrong is lost. so -black box aside- why flights depend on pilots communication for location and other flight information? what are the difficulties to send this data regularly and automatically during the flight? $\endgroup$– MarwareMay 8, 2015 at 5:46
$\begingroup$ Pfft, hundreds of lives? That's like e-9 size dent in human's genetic diversity, if that? $\endgroup$– bjb568May 8, 2015 at 22:34
$\begingroup$ The "hundreds of lives" calculation assumes that the problem is one that can be prevented (to some degree) from recurring by obtaining knowledge of its occurence, and that such prevention will happen (it might be too expensive or politically unachievable). It also fails to consider the life analog of what economists call net present value: how far in the future would we expect to wait for the recurrence to claim lives if it is not prevented. $\endgroup$– Doug McCleanMay 9, 2015 at 4:44
5$\begingroup$ It should be noted that shark tags are as hard to detect as black boxes. They're only detected when the shark swims close to the surface. When the shark dives to deeper waters the sharks essentially disappears from our sensors. We get the depth record because the tag records them to memory and transmits them the next time the shark surfaces. So basically... black boxes would be as easy to detect as shark tags if we manage to teach crashed planes to swim like sharks (But then they'd be harder to get to because they keep moving around). $\endgroup$– slebetmanMay 9, 2015 at 21:01
They're different usage cases, and have to be engineered differently. Three major points:
A shark tag doesn't have to survive a 500mph impact (#7 on the list) with the ground, and a flight recorder has to be able to do so. It adds a lot of padding and weight, and limits the kind of battery that can be used.
Sharks also don't dive to a depth much greater than 3000 feet on most occasions. A planes flight recorder is designed to survive to a much lower depth, under much larger amounts of pressure. Not to mention being designed to survive all sorts of other things.
Another point regarding depth, it is much harder to search for a signal at a depth of 15,000 ft, than it is even at a depth of 5000 ft. This article shows how big of a difference you get between even 20 meters and hundreds of meters (not thousands), it gives a good idea of what I mean.
If a shark tag fails, nobody cares. If you tag 100 sharks and 30 of the tags survive, you still have some pretty good data. But if one airplane crashes and its black box fails, it's considered unacceptable. They are required to survive 100% of the time.
All of these differences combined mean that black boxes are manufactured to much higher standards, and as a result they are bulkier, have different sorts of radios and require much more battery life (to support the larger systems) than a shark tag. All this conspires with the difficulty of getting a receiver deep into the ocean to make finding FDRs/CVRs really difficult.
That's not to say they couldn't design one that is much better, it just becomes extremely expensive (as all things are on airplanes). And you have to determine if these edge cases (like flight MH370) are worth making an airplane a few million dollars more expensive (between R&D and certification, the later being quite expensive).
I think the theory was they should be able to find any one of these within a month, and that may take some rethinking (maybe 3 months, or a year perhaps?) But they'll never be as successful as shark tags just because the requirements to be able to find one at that depth 100% of the time are quite different from the needs of a shark tag.
$\begingroup$ This answer sums up in a simple language why FDRs are designed this way, but, I was looking for one more point which is (why can't be better?) and I found it in the link you provided #8, thanks! $\endgroup$ May 8, 2015 at 3:26
$\begingroup$ Also, shark tags generally aren't required to survive being cooked in a pool of blazing jet fuel for hours on end. $\endgroup$– VikkiMar 13, 2019 at 23:49
Shark tags work by only sending the logged data when the shark resurfaces. Between those it just stores the data in memory until it can send it.
Sending underwater takes a lot of power otherwise.
1$\begingroup$ Deployable black boxes make it easier to recover the black boxes but not necessarily the plane. It would be the same situation as it was with the Titanic where we knew exactly where it sank but its resting place on the ocean floor turned out to be much harder to locate. $\endgroup$ May 9, 2015 at 21:04
$\begingroup$ @slebetman The plane is gone, people aboard died, but FDRs with GPS, proper batteries and can resurface will be helpful to lessen future accidents $\endgroup$ May 10, 2015 at 15:10
Because they're located in the wreckage, which can be at great depths. The only signal that can be sent at great depths is an audio signal, and that takes a lot of power (relatively speaking, the CVR and FDR are battery powered)
Sharks (or whales, they are often tagged) either remain in relatively shallow waters, or occasionally swim near the surface, where a radio signal can be detected.
The practical solution would be a realtime data feed of data now being recorded on the FDR to a remote receiver, sort of a super ACARS. In fact, ACARS data factored in determining the cause of the AF 447 crash long before the wreckage and black boxes were found - it showed a stall after loss of airspeed from frozen pitot tubes.