Now that the Malaysian flight was again in the news, that they had officially given up and stopped searching, this issue comes to mind again.

Why do w all depend on finding a physical recorder, and why is it so hard to find?

  1. Why isn't the system updated so that the flight recorder can live stream all its info back to the manufacturer?

  2. Why does it only give off sonar signals and not high frequency electromagnetic broadcasts which, I would imagine, would be far easier to find?

  • $\begingroup$ I would suspect something along the line of system simplicity. $\endgroup$ Jan 19, 2017 at 23:06
  • $\begingroup$ @SMSvonderTann That would be simple, until you gotta find that thing. $\endgroup$
    – HaLeiVi
    Jan 19, 2017 at 23:07
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    $\begingroup$ You've asked two separate questions at once, which is frowned on in the Q&A site format. One has already been discussed at length here. Not sure about the other. Maybe consider Why don't black boxes have their own GPS? $\endgroup$ Jan 19, 2017 at 23:21
  • $\begingroup$ Sounds like the second question is addressed here: Why don't black boxes send a signal when above water? $\endgroup$
    – fooot
    Jan 19, 2017 at 23:24
  • $\begingroup$ "[why] not high frequency electromagnetic broadcasts". Because this is better done by the ELT. But radio signals don't propagate in water, so for water there is the ultrasonic ULB. $\endgroup$
    – mins
    Jan 20, 2017 at 1:04

1 Answer 1


This should be split into two questions as mentioned. The First one is addressed elsewhere on this site but the second one is worth noting.

Why does it only give off sonar signals and not high frequency electromagnetic broadcasts which, I would imagine, would be far easier to find?

The short answer: high frequency waves don't propagate through water very well (or very far for that matter).

This in turn prevents underwater signal broadcasting units from using any kind of high frequency wave. Thus you need to operate in the audible or just above audible range to get effective underwater range. Subsequently the Shannon Theorem limits how much data can be bussed over a low frequency wave. As such black boxes can often do nothing more than emit a simple ping.

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    $\begingroup$ The quoted question asks about high frequency EM waves, while your link refers to acoustical waves. $\endgroup$
    – BowlOfRed
    Jan 20, 2017 at 0:23
  • $\begingroup$ Communication with submarines $\endgroup$
    – Steve
    Jan 20, 2017 at 0:51
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    $\begingroup$ @BowlOfRed, the same applies to EM, only more so. Radio communication with submarines is done using single-hertz radio frequencies. $\endgroup$
    – Mark
    Jan 20, 2017 at 3:38
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    $\begingroup$ @BowlOfRed: Just to give an idea: the antenna for a ground station for communication with submarines is typically about 60km(!!!) long, and the ground stations typically have their own power plant(!!!). And what about the other direction? Well, actually, submarines can't answer, it is simply impossible to put an ELF transmitter on a submarine (which after all is huge and has its own nuclear power plant), so obviously it is even more infeasible to put in a small FDR/CVR. $\endgroup$ Jan 20, 2017 at 10:14
  • $\begingroup$ @JörgWMittag Thanks. Although I found this idea among answers referenced by fooot I didn't see this issue directly addressed. $\endgroup$
    – HaLeiVi
    Jan 20, 2017 at 19:40

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