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huncowboy
19th Apr 2011, 14:02
If I plug into the CVR test inlet on the overhead panel I can hear the other guy talking into his hot mike. All this while the CVR button was in auto and when the CVR should have been off according to the logic. Does that also mean the CVR is recording this? I doubt, but is sure made me wondering.

Avionker
20th Apr 2011, 00:08
What exactly were the conditions at the time?

huncowboy
20th Apr 2011, 00:11
CVR pushbutton in AUTO ("blue on light" off). Fully powered on external power, engines shut down at the gate. Basically during a turn just shortly before push.

Avionker
20th Apr 2011, 08:03
Not in work today but will have a trawl through the manuals tomorrow.

mcdhu
20th Apr 2011, 08:09
I think the manuals say that the CVR powers up during the first 5 mins after electrical power is applied to the ac ie you don't need to press the CVR Auto Pb to make it work before engine start. What do you guys think?
As with many parts of the FCOM, it is not written clearly.

Cheers
mcdhu

vapilot2004
20th Apr 2011, 08:33
I've been told that monitor jack is in the analog loop.

Ndicho Moja
20th Apr 2011, 09:19
Nothing being recorded but the mike is still open.

tvrao
25th Apr 2011, 13:15
The CVR power logic is controlled by relays which in turn depend on engine low oil pressure switches and landing gear compressed or not compressed sensing switches connected to LGCIUs(Landing gear interface control unit.
If these relays are not operating correctly , you can get this type of problem.
What you hear from CVR jack on overhead panel is what is actually being recorded after delay of about half a second.This is possible if your CVR is powered .
In the scenario you described it could be that you might have plugged in CVR jack within 5 minutes of last engine shut down or within first 5 minutes of application of external power to aircraft electrical network.
other possibility is defective relays.This not desirable as the same set of relays are also controlling the flight data recorder and there is a possibility of losing valuable recording when it is not intended to be powered.
You can write your observation in the tech log,maintenance engineer will be able to fix the problem.

Avionker
25th Apr 2011, 19:22
There is no problem as far as I can see. To prove this for yourself plug in a headset and listen. Talk so the area mike or a boom mic picks up your voice, make sure the parking brake is set, and push the erase button for half a second or so. You will hear a tone indicating that a bulk erase is in progress. If you hear this tone the CVR is not recording.

The CVR is powered up whenever the CB is in, as is the FDR. Just because they are powered up and are been fed data does not mean they are recording it.