B737-8 CVR Recording on APU?

[aviationgeek007]

Hello and Greetings.

I am presently in the midst of a debate which I believe an expert in B737-8 could shed some light on.

We had a minor accident on the ground with a B737-8, 2016 make.

Our airline technical team are contending that the relevant cockpit voice recording was overwritten after the accident because the APU kept running for over an hour after the accident.

The civil aviation technical team are of the opinion that since the engines were turned off coincident with the accident therefore the recording should have been preserved up till that moment. They are also arguing that modern day aircrafts such as the one in question record much more than an hour of CVR.

Please guide if you are aware of the technicalities of the CVR on a B737-8.

Thank you

[Exup]

VOICE RECORDER - GENERAL DESCRIPTION General The voice recorder unit makes a continuous record of flight crew communication and flight compartment sounds. It erases the communication data automatically so that the memory stores only recent audio. The voice recorder unit keeps the last 120 minutes of communication data in memory. The voice recorder unit receives audio from the remote electronics unit (REU) and the area microphone. The area microphone is in the cockpit voice recorder panel.

It mentions auto erase but not sure after what period of time this happens, so it appears they could be correct.

[Dougie_diesel]

Or had it even started recording yet?

[B2N2]

If there was an 'incident' you should be asking Boeing this question.
The CVR is likely on a standby bus therefore powered by the APU if the APU is selected as the electrical power source.
The CVR circuit breaker probably should have been pulled to preserve the data.

[CallmeJB]

CVRs aren't really meant to be used in an investigation involving discipline, if that's what this is a part of.

[Avenger]

The CVR will normally start recording approx 5 minutes after the aircraft is energised and keep recording until 5 minutes after the aircraft is de-energised. In your scenario only the last 30 minutes would be available, but if the "incident" took place in the first few minutes and then the APU was left supplying the buses it would not be available, assuming the aircraft was energised all the time the APU was left running.

[NSEU]

It depends on the individual aircraft. There are 737NGs which only start recording when the engines are at idle power or above until 5 minutes after engine shutdown. There are other 737NGs which record whenever there is electrical power on the aircraft. I'm sure your technical team is well aware of the type of Voice Recorder system fitted to their aircraft. The Civil Aviation experts won't know which type is fitted unless they have access to the same information your technical team has.

[aviationgeek007]

First of all, thank you very much for the replies.

We have been informed by the Civil Aviation that whatever the model of the CVR, the pilot is required to pull the CVR circuit breaker after an incident has taken place.

Is there any reference from Boeing on this or it varies from airline to airline? Would we be violating any rules if our procedures didn't require the circuit breaker to be pulled?

[RAT 5]

Curious there are differences in the operation of the CVR. I would have expected that, as the FDR & CVR are mandatory requirements under the FAA or EASA to help accident/incident investigation, their operating specifications would be the same for all types. I can understand that those specs might change with time; maybe that is how the differences occurred??

[Avenger]

We have been informed by the Civil Aviation that whatever the model of the CVR, the pilot is required to pull the CVR circuit breaker after an incident has taken place. Never heard of such a procedure, this appears to be a fishing exercise or digging for a way out option.. No Boeing procedure on this and I would not advise this in any event. If it was required it may be mentioned on the QRH evacuation C/L for instance.
NSEU/RAT some have CVRs that start either when AC power is supplied to the bus OR when the oil pressure switch records > 5psi ( according to the tech bods!) guess its for the battery start condition.
Abstract:
One commentator (ECA) proposed to reinstate the former provision of paragraph OPS 1.085 of EU OPS, that allowed the commander to deactivate the CVR in flight in order to preserve the recording of a serious incident. This provision had been removed prior to NPA 2013-26, based on a recommendation of the Flight Recorder Study Group (FRSG) of the Joint Aviation Authorities, before the rulemaking competence for air operation rules was transferred to the Agency. The FRSG considered that, in case of a serious incident, it was preferable to keep the CVR activated and lose the relevant part of the recording, rather than running the risk that the serious incident develops into an accident and audio essential for understanding this accident is missing because the CVR was deactivated. For this reason the ECA proposal has not been accepted.

[Piltdown Man]

We are required to preserve CVR/FDR evidence after an incident, if we remember. We do this by "tripping" the appropriate (electronic) C/B. Being short haul this is rarely, if ever, done in flight. However, we have two combined jobbies fitted so turning one off still means compliance with an appropriate legislation. Although a different type, our CVR data records a forever rolling two hours of data whenever the aircraft is powered. Another type records (a rolling 30 minutes or two hours, depending on fit) whenever any fuel shut off is open or the CVR over-ride is pressed.

[Airbubba]

Curious there are differences in the operation of the CVR. I would have expected that, as the FDR & CVR are mandatory requirements under the FAA or EASA to help accident/incident investigation, their operating specifications would be the same for all types.

A lot of the stuff that is aircraft manuals about the CVR is incorrect from what our safety guys have told us. The two hour requirement came into effect for U.S. airliners about five years ago. Our manuals still had 30 minutes in some places until recently.

On some aircraft, the CVR runs anytime there is power on the plane. Or so I've been told. We have a shutdown checklist procedure to pull the CVR breaker after certain 'reportable' events.

Remember the 'erase' button? In the old days we were told that it erased the entire recording. Pilots , e.g. Harvey 'Hoot' Gibson, would forget not to push this button after an incident in many cases. ;)

Now the button only erases all except the final 30 minutes it seems from these excerpts of FAA regs:

§ 121.359 Cockpit voice recorders.

(f) In complying with this section, an approved cockpit voice recorder having an erasure feature may be used, so that at any time during the operation of the recorder, information recorded more than 30 minutes earlier may be erased or otherwise obliterated.

(i) By April 7, 2012, all turbine engine-powered airplanes subject to this section that are manufactured before April 7, 2010, must have a cockpit voice recorder installed that also -

(2) Retains at least the last 2 hours of recorded information using a recorder that meets the standards of TSO-C123a, or later revision; and

(3) Is operated continuously from the use of the checklist before the flight to completion of the final checklist at the end of the flight.

(j) All turbine engine-powered airplanes subject to this section that are manufactured on or after April 7, 2010, must have a cockpit voice recorder installed that also -

(2) Retains at least the last 2 hours of recorded information using a recorder that meets the standards of TSO-C123a, or later revision; and

(3) Is operated continuously from the use of the checklist before the flight to completion of the final checklist at the end of the flight.

https://www.law.cornell.edu/cfr/text/14/121.359

And, as with other devices in the digital realm, there is some doubt, in my mind at least, whether the erase function actually works or whether the erased recording can be recovered. A coworker learned the hard way that reformatting an SD card doesn't totally remove pictures of a Thai girlfriend. :eek:

Some comments here from pilots at overseas airlines seem to indicate that the erase button may be disabled totally in some installations. Also, it is claimed that some non-U.S. carriers 'audit' the CVR recordings to ensure compliance with SOP's and the like. The U.S. NTSB has asked for this ability, along with cockpit cameras for a while now.

[Skyjob]

Some operators require their crews to switch the Voice Recorder ON on ground operations thus overwriting anything recorded prior.

The length of recording depends on actual one fitted, with several options to choose from, thus depending on installation your total available duration varies.

The combination of the above makes it impossible without further knowledge to advise how long a recording is available and whether it should be preserved or not.

Note 1: the airlines that required the CVR to be ON during ground operations usually have SOP's in place to pull CVR after checklist complete in case of accident/incident.

Note 2: there is a reason for pulling CVR CB during evacuation...

[Nator]

I used to fly for an Operator which had a modified Secure Procedure to include pulling the CVR´s CB.

The reason was purely punitive, but anyway I guess it implies that The CRV keeps recording after you leave the A/C to the Engineers with the APU running.