rfields5421 From United States of America, joined Jul 2007, 6810 posts, RR: 29 Reply 1, posted (4 months 3 weeks 3 days 7 hours ago) and read 3386 times:
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.
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!
golfradio From Canada, joined Jun 2009, 658 posts, RR: 2 Reply 7, posted (4 months 3 weeks 22 hours ago) and read 2488 times:
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.
celestar345 From Hong Kong, joined May 2013, 19 posts, RR: 0 Reply 8, posted (4 months 2 weeks 1 day 6 hours ago) and read 1908 times:
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...