whiplash
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Why Only 2 Hours Of CVR Data?

Sat Jul 13, 2013 7:18 am

Why is the minimum requirement for CVR recordings only 2 hours compared to the FDR, which records upwards of 25 hours?

Is it cause the CVR data is heavy, and the equipment cannot record more?
Or is it cause CVR data older than 2 hours, would not be more helpful in case of a crash/incident?


 
 
rfields5421
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RE: Why Only 2 Hours Of CVR Data?

Sat Jul 13, 2013 12:25 pm

The CVR two hour time frame likely came from equipment limits back when they were real tapes used to record data.

Some folks object to recording more voice data because they don't think it is ever relevant to investigations. Some CVR data has been used by airline management to 'spy' on pilots in the past. There is also a concern about a desire by airline management to 'grade' pilots based on who is the most efficient fliers based on FDR data.

Those are some of the reasons to objections against recording more than two hours.

There is not technical reason modern digital CVR devices which store the data on solid state chips (similar to a thumb drive) could not record more.
 
N747PE
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RE: Why Only 2 Hours Of CVR Data?

Sat Jul 13, 2013 1:05 pm

The truth is crash investigators can only listen to just so much snoring     
 
pilotpip
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RE: Why Only 2 Hours Of CVR Data?

Sat Jul 13, 2013 3:53 pm

Modern ones usually record much more than 2 hours.
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Starlionblue
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RE: Why Only 2 Hours Of CVR Data?

Sun Jul 14, 2013 1:23 am

Why would you need more? It is very unlikely an accident will unfold for more than 30 minutes. Japan Airlines 23 was an exception but they had contact with ATC.

I suppose the DFDR needs longer recording times because something can be wrong with system in a latent fashion.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
EGGD
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RE: Why Only 2 Hours Of CVR Data?

Sun Jul 14, 2013 8:16 pm

Quoting Starlionblue (Reply 4):
Why would you need more?

Good question. In the event of an accident/airframe loss/crash then 30 minutes is more than sufficient. The problem with 30 minutes comes with a serious event that happens on a commercial flight that requires a detailed investigation by the relevant authority. This serious event could happen at any stage of flight and whilst requiring investigation may not result in the CVR 'ending' at the point in time that said event occured. Just as a random example an airline stalling on final approach and subsequently recovering. Flight Data Monitoring would pick up the event but unless the crew took action to preserve the CVR the data may be wiped by the time the aircraft's engines are eventually shut down. In my opinion the CVR length of recording should be of a suitable length to cover the length of any sector flown, I don't see it is a major difficulty to implement and certainly if there is a significant event any CVR could be 'fast forwarded' to the appropriate point without the need to trawl through hours of laborious and inane chatter from the flight crew!
 
Kaiarahi
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RE: Why Only 2 Hours Of CVR Data?

Mon Jul 15, 2013 4:05 pm

Quoting Starlionblue (Reply 4):
Why would you need more?

AF447 is an example. A longer recording may have given an indication of why the crew was so dysfunctional (i.e. interpersonal relationships). This is probably true of many CRM incidents.
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golfradio
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RE: Why Only 2 Hours Of CVR Data?

Mon Jul 15, 2013 9:12 pm

I guess the only accident where the investigating authority wished for a longer CVR recording was the QF32 one. In that case engine #1 could not be shut down and the CVR continued recording and erased the recording during the incident. I believe they expressed the wish only for the purposes of understanding ideal CRM practices and noted that this did not have any bearing on the actual investigation.
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celestar345
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Joined: Wed May 08, 2013 5:35 pm

RE: Why Only 2 Hours Of CVR Data?

Mon Jul 22, 2013 1:16 pm

Quoting rfields5421 (Reply 1):
Some folks object to recording more voice data because they don't think it is ever relevant to investigations. Some CVR data has been used by airline management to 'spy' on pilots in the past. There is also a concern about a desire by airline management to 'grade' pilots based on who is the most efficient fliers based on FDR data.

If my memory serves me right, Once the engines are off and park brake set CVR data can be erased in the cockpit via a pushbutton on the overhead panel...
 
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HAWK21M
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RE: Why Only 2 Hours Of CVR Data?

Tue Jul 23, 2013 10:16 am

Quoting celestar345 (Reply 8):
If my memory serves me right, Once the engines are off and park brake set CVR data can be erased in the cockpit via a pushbutton on the overhead panel...

True....But a DGCA Mandatory mod has required that the erase circuit card be disconnected to avoid erasure.

On the OP.......2 hrs is adequate as it will be used to investigate an Accident/Incident only.
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