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Recording the thousands of parameters and voice conversations must take a huge amount of storage, and so I am wondering, how frequently is this data "deleted", so it can be used again?

For example, after every successful flight, is the CVR and FDR data deleted or it records maybe 10 flights or so, and then is reset?

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  • $\begingroup$ This seems useful: quora.com/… $\endgroup$
    – Ezra
    Commented Dec 10, 2017 at 16:56
  • $\begingroup$ Related $\endgroup$
    – Pondlife
    Commented Dec 10, 2017 at 18:01
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    $\begingroup$ They record on a "loop" so that the oldest data is automatically overwritten by the latest data. The number of flights depends on how long each flight is, and sometimes is only part of one flight. As far as how long, there are different rules for different aircraft, and probably different rules for different countries. Do you have a specific set of regulations that you are asking about (US/FAA, Eurpoe/EASA, or somewhere else)? $\endgroup$
    – Lnafziger
    Commented Dec 10, 2017 at 20:37

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No, they are not reset after each flight, but as commented, the FDR and CVR are on a loop, and just keep recording over the old data. For US registered aircraft, FAA Regulation "14 CFR 91.609" covers flight data recorders and cockpit voice recorders.

It states for flight data recorders:

(c) 1. No person may operate a U.S. civil registered, multiengine, turbine-powered airplane or rotorcraft having a passenger seating configuration... of 10 or more that has been manufactured after October 11, 1991, unless it is equipped with one or more approved flight recorders that .... are capable of retaining no less than 8 hours of aircraft operation.

And:

(c) 3. All airplanes and rotorcraft subject to (the above)... manufactured on or after April 7, 2010, must ... retain at least the last 25 hours of recorded information...

For cockpit voice recorders:

(h) 2. All airplanes required by this section to have a cockpit voice recorder and a flight data recorder, that are manufactured before April 7, 2010, must by April 7, 2012, have a cockpit voice recorder that also ... retains at least the last 2 hours of recorded information ...

There are not "thousands" of parameters.

The CVR must record the following 25.1457 (Cockpit voice recorders):

(1) Voice communications transmitted from or received in the airplane by radio.
(2) Voice communications of flight crewmembers on the flight deck.
(3) Voice communications of flight crewmembers on the flight deck, using the airplane's interphone system.
(4) Voice or audio signals identifying navigation or approach aids introduced into a headset or speaker.
(5) Voice communications of flight crewmembers using the passenger loudspeaker system
(6) all datalink communications

So, probably 6 or so channels.

For the FDR, wikipedia states "There are 88 parameters required as a minimum under current US federal regulations (only 29 were required until 2002), but some systems monitor many more variables."

So, if the flight lasts less than two hours, there will be at least the whole flight on the CVR. But if the flight is longer than two hours, you only have the last two hours.

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    $\begingroup$ I recall seeing at least some flight deck photos showing a CVR erase switch, allowing the crew to erase what's on the cockpit voice recorder. Maybe you can comment on that? $\endgroup$
    – user
    Commented Dec 13, 2017 at 12:23
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    $\begingroup$ The standard (EUROCAE ED-112) provide for a means to erase voice and video recordings following completion of a flight. Interlocks prevent erasure before the aircraft has landed safely (on ground, engines off). Mostly political so that idle comments made in flight aren't used by the airline against the pilots. Not too likely though as the CVR has to be removed from the a/c before any recordings can be offloaded. $\endgroup$
    – Gerry
    Commented Dec 13, 2017 at 14:23
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    $\begingroup$ @Gerry You don't need to remove the CVR or FDR for a readout. You just need a laptop or special PDA. Readouts have to be done regularly by maintenance to ensure they are operational. $\endgroup$
    – user71659
    Commented Dec 13, 2017 at 17:16
  • $\begingroup$ FDRs are not required to record thousands of parameters. However, some FDRs (especially newer ones installed in newer aircraft) do record thousands of parameters, in the name of air safety. $\endgroup$
    – Vikki
    Commented May 25, 2020 at 21:51

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