Re: RAT for CVR

Date:         05 Oct 98 00:26:15 
From:         k_ish <>
Organization: ICGNetcom
References:   1 2
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S.L. wrote:
> David Lesher wrote:
> > There are very valid reason for not putting the CVR onto the
> > last-chance emergency battery bus, but how about on its own
> > deployable ram air turbine?
> No, it shouldn't be on a bus at all, nor on a RAT. It *should* have an
> internal lithium battery backup so that it will continue operating even
> if you rip it out of the aircraft, IMHO :-) So should the DFDR- even if
> its inputs lose power and fall off-line, the recorder itself shouldn't
> be the weak link.

One fatal flaw with any battery backup, that has been pointed out in this
NG before.  A CVR is on a 30-minute loop; a FDR is on a longer loop,
probably several days.  If the battery backup had continued to run on
SR111, by the time the recorders were recovered, they would have contained
no data instead of missing the last 10 minutes.  Additionally, the last
"time stamps" on the CVR and FDR could provide valuable data on how the
failure(s) progressed.

Also, a lithium battery of the capacity required to power an FDR becomes a
substantial hazard in itself.

Design a safe source of backup power that knows exactly when to shut itself
off under any and all crash scenarios, and the NTSB will beat a path to
your door.

Ken Ishiguro