737 Ng Cvr
 

Could one of you immensly clever tech chaps answer a quick question that caused civil war in a recent tech refresher.

On the 737NG when is the CVR active, we have found 2 references both valid. One is "when even 115v AC is applied to the aircraft", choice B is "from engine start (due to rising oil pressure triggering the cvr switch) until 5 mins after shutdown.

Answers on a postcard please.

Many thanks in advance.

F-C

You can plug in your headset to the test jack on the P5 and listen to the audio inputs into the CVR anytime a.c. power is on.
Now I dont have our schematics in front of me but the inputs are active without oil pressure.Is it recording though?
The 115vac answer sounds best to me.There are a few nasty configs I can think of where you have no oil pressure but still flying.It would be handy to hear what was going on in the cockpit under those conditions.

Someone will have the schematics available for definitive answer.

It is powered when AC power is available as stated above. It records from either placing the CVR switch to ON or latest engine start (oil pressure) until 5 minutes after last engine shut down. If you switch it ON manually the switch trips to AUTO once oil pressure triggers the normal recording logic.

ampclamp guess is correct i.e. anytime there is 115V AC power (operates when transfer bus #2 is powered). Monitor indicator pointer deflection confirms recording (or erasure) on all 4 channels with 1s delay.

Hi denti.
worked on buses with that feature but not our model -800's.
No such thing as a "standard" model out there which makes these forums an interesting place.Always something different.

Thanks for the input all.

As ever with tech questions, the answer is the one that is most correct or in some cases least wrong.

Have read that the oil pressure trigger auto function is an "option" right up there along side wings and loo seats. Our version has the cup holders, and the 12 CD changer with boom box so does have the oil pressure thing, (complicated technical terminology).

Well at least until the tech pilot says otherwise.

cheers
FC

Yeah, as i mentioned somewhere else here, boeing is one of very few companies that offers a longer option list than porsche does. And even more expensive too. Just weird that with around 10 or so different configurations in our fleet all have that little oil pressure thingy, but probably you can pin program that behaviour, im only a pilot, not an engineer ;)

FC, my quote was from an "unofficial source" possibly the same one you used.

When I got off my lazy couch I found your second option -from 1st engine start to 5 min after ...- in my OM. And BTW, no trace of the deviation pointer on our a/c.

We have BOTH systems in our fleet.
In the Leased birds, the CVR starts automatically after 1st engine start [N2 >50%]. The acft is also provided with a "Voice Recorder" switch which has 2 position - ON and AUTO. As part of our Pre-flight procedures, the switched is moved to the ON position. As the 1st engine accelerates through 50% N2, it automatically moves to the AUTO position. The CVR stops automatically 5 min after last engine shutdown.

In our own acft, the CVR runs as long as AC power is avbl. And the "Voice Recorder" switch is also not installed.

Hope this helps