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Question for AJ about CVR.

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  • Question for AJ about CVR.

    I have a question for AJ (or anyone who knows) about cockpit voice recorders. What is it that makes the voice recorder start recording? I've been thinking about this, and I wouldn't think that in a bad emergency the pilots would be reaching around to find the button that makes it start recording. Does it start when a certain number of things happen to the plane? Or is it always recording for the entire flight.
    And a follow up for anyone. Does anyone know if there are CVR recordings of Southwest flight 1248. If there are, have they been made public and are they on the internet anywhere?


  • #2
    They are always recording. Do newer CVRs record more than the last 30 minutes? With new recording media, you'd think it could be extended quite a bit over the old tape media. Are there digital CVR/FDR units now?

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    • #3
      The recorder is always recording, at least when there is power going to it. It runs on a loop, basically, with the older magnetic tape recorders looping every 30 minutes, and the newer digital recorders recording on longer loops. There have been incidents in the past where more than 30 minutes elapsed from an initial event to loss of power to the recorder (impact, electrical failure, etc.) and critical data was overwritten due to this loop.

      To prevent this, most airliners have a CVR stop switch that can be activated by the flight crew to stop the CVR after an event and prevent 'looping over.'

      I don't know if there is any CVR data for the Southwest event at MDW (I would imagine there is), but if there is, a public transcript will be released by the NTSB in due course. The release of actual CVR audio recordings by the NTSB was outlawed by Congress in the early '90s.
      Trump is an idiot!
      Vote Democrats!!

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      • #4
        If there are outlawed how is it legal for airdisaster.com to have CVR recordings on their website? Are they only allowed to put a small clip of it on there?

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        • #5
          Jordan, transcripts are fine but recordings depicting actual voices are not for obvious reasons.

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          • #6
            Originally posted by JordanD
            If there are outlawed how is it legal for airdisaster.com to have CVR recordings on their website? Are they only allowed to put a small clip of it on there?
            Could be recordings that were made before the law was passed are ok.

            Does a FDR have a "stop" switch like a CVR does? Or could a crew just hit a breaker to deactivate it?

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            • #7
              Originally posted by JordanD
              If there are outlawed how is it legal for airdisaster.com to have CVR recordings on their website? Are they only allowed to put a small clip of it on there?
              Take a look at the recordings available on AirDisaster.Com from U.S. accidents:

              Air Florida 90: 1982
              Delta 1141: 1988
              Delta 191: 1985
              Northwest 255: 1989
              United 232: 1989

              All of these recordings were released before present laws were in place.

              That being said, a CVR unit and the recording contained are still property of the airline even after an accident. Thus, should an airline choose to do so, they can make the entire recording public. That is exactly how the UA232 recording was released -- United chose to do so, to publicly show the heroism displayed by its flight crew.

              The DL191 was recording was released as a result of a lawsuit (although I'm not familiar with the details regarding this).

              I don't know how/why the other recordings were released, but somehow, they were obviously made public.
              Trump is an idiot!
              Vote Democrats!!

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              • #8
                Haha, This was actually a question in one of my Engineering Exams...

                "From what point in time do the CVR's commence the recording of data?"

                a) On Battery Power-Up
                b) Upon all engines being started
                c) Crew Action as per check-list

                The answer of course is A. On most modern aircraft, the moment you push the battery "ON" switch, the CVR's are ready to record data. I think you used to be able to erase the data upon landing, however they dont allow that anymore after a chinese crew at Cathay Pacific erased the data when they f*cked up an approach...

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                • #9
                  The CVR breaker must be pulled after any NTSB reportable incident / accident. Its actually on a checklist that way with us.

                  I'm not sure we have guidelines as to when we're allowed to erase a CVR, although there is a button for it installed on the CVR control head.

                  FDR has similar functions, but no erase switch. That is switched on by the beacon switch, or weight on wheels in my a/c if you forget to turn on the lights.
                  Bite me Airways.....

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