CVR why 30 minute duration?
 

As we all know data storage costs have plummeted over the years, however the standard CVR (still) only records the last 30 minutes. Is there any reason why this is limited, other than the cost of re-engineering/re-certifying a new recorder design?

It seems there have been a few instances where the 30 minute limit has not been sufficient to capture a particular circumstance (for example Northwest 188).

- GY :8

Our is 2 hours...

It's the cost of re-equiping, not redesigning and the certification of the new 2hr ones is done.


If you want a quik fix, then it probably will require a recertification, and not sell very many since it's still "old"

On the other hand the present 30 min CVR still meet the cert standards for in-service use.

What a/c?

Thanks, GY

On the A320 family

Copy and paste from our FCOM "Only the last 2 hours of recording are retained."

All modern units are two hours.
Ejets 2 hours voice 25 hours data in a single unit. Each aircraft has 2 fitted.

Old A320's have the 30 min CVR but since around 1997 they have been fitted with a 2 hour CVR.

only 30 mins
 

Believe in was a union agreement between BALPA and the CAA.

It was a recommendation included in the public inquiry into the Papa India disaster when a Trident 1 stalled after take off at LHR in 1972.

A lot of BEA pilots had a distrust of management and the agreement included the facility to erase the tape after engine shut down.

I flew with the system for three or four years after it's introduction - it was ALWAYS erased (or so we thought!)

30 minutes is normally longer than aircraft take to crash? Therefore it will cover 99% of the crashes which is what it is there for. Not for listening to in court while the crew discuss the incompetent DFO as they taxy out before crashing 4 hours later...

Point taken, but why the longer record period for the the FDR? Seems the same reasoning would apply...:confused:

- GY

Hi GY,

Sometimes the holes in the cheese started to line up hours before the accident / incident.
e.g. The 737 from Cyprus when they misidentified the cabin altitude warning horn for the config warning or the A330 Azores glider when the fuel leak was mis diagnosed as an imbalance problem. The CVR helps the AAIB (or equivalent) understand "why" as well as "what" happened.

is irrelevant.

rudderrudderrat: Thanks for that - it seemed to me the chance that problems sometimes occur quite some before any incident was quite possible, and of course simply having a longer recording does not mean you have to listen to it all.

There's also the thought that if you have nothing to hide...

- GY

Rudderrudderrat...
 

No, it's absolutely not irrelevant.

IGh: Ok, well that's a little more "with it". The reason I was stuck on the 30 min record period, was that the current issue of A320 data package (issued to simulator manufacturers) only references a 30minute record period, and similarly the current Boeing 737NG data package is the same.

In reality, the CVR aspect on a sim is of minor significance, so overall not a big deal.

- GY

GY,

Is that 1.7?

I guess the 30 minutes is also enough time to record the approach brief. Are there any rules or SOP's out there preventing a brief not before 30min ETA?

I have often thought it very strange to only have 30mins / 2 hours recorded given what technology can do now.

You often hear of incidents and the cvr has been over written after landing because nobody has pulled the circuit breaker.

There have also been incidents at the start of long haul flights and no record left by the time they land e.g the aircraft (A340?) that took off in Alaska on the taxiway and left wheel marks in the snow bank at the end.

IIRC the CVR was no use in determining if it was a heated debate with laptops or if the guys really had fallen asleep over the States earlier this year.

If you can record 25hrs FDR surely you can record 25hrs CVR.

Yup, LiveATC files have low bitrate, so they can store 30mins in about 3 or 4mb. It shouldn't be a big deal considering today's technology. Does anyone know the storage capacity of solid-state recorders?

The period is low despite the far greated recording capability with solid state units because of pressure from the unions who would rather conspire against safety and let a few more of their members and hundreds of the public die than show up the incompetence of live members

While longer time would rarely aid accident investigations it would make incident investigations far better and prevent more accidents (and deaths) in the first place.

It is time that routine CVR monitoring was introduced to catch rogue pilots before they kill, encourage compliance by all pilots and help fault find faulty recorders.

Shell thingy,

It's time you were banned.

You think you're being clever and 'challenging' and you come up with some of the stuff tripped out by many of those who make a good living in 'safety', but then you let yourself down with a post like that above.

If you were the sort of person your online persona claims you to be, you would know that CVRs are very routinely overwritten after incidents, and that a longer duration would be of daily benefit to investigators.

Stop wasting our time here with your silly little meanderings please. You're spoiling the place for those of us who DO know what we're doing.