Equipment redundency and certification

[212man]

This may not be the right forum but as many here will be directly inolved in aircraft certification I thought I'd try.

I recently read the Portuguese accident investigation report on the Transat A330 that ran out of fuel and landed at the Azores. What struck me the most was how on earth it is/was possible to certify an aircraft with back up systems that resulted in there being no FDR or CVR? If a large airliner is flying with its sole power being the battery and RAT it must be, by definition, in a very precarious position and chances are that, even if a safe outcome results, an AAIB investigation will be needed. A CVR and FDR would seem a pre-requisite in this case!

I would aslo have thought losing the DME wasn't too clever either; it can't be that power hungry, surely?

Reminds me of the acceptance flight, of a new helicopter, I made a few years ago when on shutdown we found there was a HUMS failure. Further investigation showed that the manufacturer had powered the HUMS DTU though the shed bus!

[DFC]

DME and Transponder (especially the old types) are the most power hungry radios in the aircraft. Transmitting on the HF and then transmitting on the VHF are also high on the power usage list. As far as I remember the DME and Transponder are above the HF radio because they transmitt almost all the time.

Regards,

DFC

[Mad (Flt) Scientist]

Given a choice between an active FDR/CVR to enable someone to investigate an accident (because it drained too much power and the a/c lost electrics in a glide, say) or having the aircraft survive but not know exactly why because the FDR/CVR were off, I pick the latter every time.

The FDR/CVR are not safety critical for the souls on board and should not be treated as such.

[Paul Wilson]

Should not the CVR if not the FDR have an internal battery to keep it running for say 1 hour after power loss? Totally separate from on board power, and with recent battery technology we're not talking a great lump of a battery.
So that you can still "pull the C/b" following an incident run power to it from two systems, batt. only kicks in if both power inputs go dead, if primary goes dead it assumes you have deliberatly disconnected it and stays off.

[212man]

I agree that the FDR/CVR should not consume power to the detriment of occupent safety; obviously. I still would have thought in this day and age it should be possible to maintain both.

Although not directly applicable, look at the controversy surrounding the Mull of Kintyre Chinnok as a result of having no FDR/CVR at all. Not fitted or not powered; the outcome is the same (lots of extra work, speculation and possible controversy).