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I never knew much about airplanes before the tragic incident of Malaysia 370. I have been spending a lot of time on Twitter reading various articles and investigations; in one of the articles I read, they stated that unlike transponders, "black boxes" cannot be turned off.

However, each ELT is specifically designed for each aircraft, so it cannot be tampered with. You also cannot turn off the black box, as it runs throughout the flight, recording every 30 to 60 seconds.

Is it really impossible to turn off the black boxes from within the plane?

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4 Answers 4

up vote 16 down vote accepted

There is no switch for the FDR, but there is a circuit breaker and by pulling this you are removing aircraft power from the FDR. However, this does not mean you are necessarily turning it off, as some FDR can be equipped with an internal power supply as a backup to aircraft power.

The quote in the question (bolded emphasis mine):

You also cannot turn off the black box, as it runs throughout the flight, recording every 30 to 60 seconds.

is a case of an "expert" or journalist confusing the lack of an on/off switch as an inability to turn something off. As you'll find many examples of in the media, they don't always get it right. The circuit breaker may not be a true on/off switch, but pulling it does accomplish de-powering (assuming no internal power supply) and thus turning off the FDR.

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in context to your answer, could you please see this ? en.wikipedia.org/wiki/… –  Sufiyan Ghori Mar 17 at 20:36
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@SufiyanGhori That is just an example of someone pulling the FDR circuit breaker. As I mentioned in my post, some FDR may have an internal power supply, but I don't have any statistics on what percentage of the installed base does. For those that dont, just as in your example, it stops recording because it is turned off. –  casey Mar 17 at 20:54
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the biggest problem with an internal power supply it that is can fail with potentially catastrophic results –  ratchet freak Mar 17 at 20:57
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@ratchetfreak I'm not debating the merits of an internal power supply, I'm merely mentioning them to cover my bases in that "pulling the breaker == off" may not be true in 100% of cases. Certainly in the plane I'm most familiar with we did not have that and if you pulled the breaker the FDR turned off and you got an EICAS message indicating DFDR FAIL. –  casey Mar 17 at 20:59
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@SufiyanGhori see the edit to my answer. –  casey Mar 18 at 2:38
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Generally, I'm pretty sure there's no switch for a Flight Data Recorder on the overhead panel in most aircraft, since I think it switches on automatically. However, i'm pretty sure that you can pull the corresponding fuse behind the cockpit. It's a safety thing after all, since you don't want a short circuit from the FDR causing problems to the rest of the plane.

While I'm not sure of how this works on the Boeing 777 as in MAS370, it was attempted on FedEx flight 705.

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I vaguely recall an accident where they concluded someone pulled the breaker for the CVR; so it was certainly possible on that type of aircraft whatever it was. Can't remember which thought. Also, the FedEx flight; but that one got reset, so it was never really turned off. –  falstro Mar 17 at 18:38
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@roe both breakers can be pulled which is what happened in Silkair Flight 185 –  ratchet freak Mar 17 at 20:20
    
Ah, right, Silkair 185 was the one, thanks. –  falstro Mar 18 at 6:46
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On most commercial aircraft there is a circuit breaker for the cockpit voice recorder. The recorder can record communication in the cockpit for 30 minutes or up to two hours on later model aircraft. They are continuous loops which will record over the oldest previous recordings. Whenever any incident occurs during the operation of a flight, the circuit breaker is pulled to keep the pertinent cockpit conversation on record and not be recorded over. I am unaware of any such circuit for the flight data recorder.

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Neither the FDR CB nor the CVR CB are accessible from the B772 flight deck. The FDR is powered on at engine start. In the event of a mishap the CVR CB is pulled as a means of saving the data. The CVR CB is accessed from the E&E bay.

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