First things first:
Originally Posted by linedriva
I'm basically trying to work out if I can legally continue on an ETOPS plan if I get a pack failure after dispatch (according to the company), but before takeoff if the MEL says no to ETOPS.
Technically, you could continue as the MEL is no longer applicable post-despatch until such time as you complete the flight. Legally, I believe the question of reasonable behaviour would subsume the technicality. I know that my first thought would be to question whether I want to take that problem airborne in all of the relevant circumstances, regardless of what the MEL says. Only if I decide that threshold question in the affirmative would I bother to see if I am permitted by the MEL to do so.
In Oz, "despatch" occurs when the aircraft first moves under its own power for the purpose of taking off, which is the legal definition of the start of "flight time". In effect, it attempts to practically recognise the point at which Ground Handling operations by the operator have, for all intents and purposes, ceased and the aircraft is solely in the hands of the Captain. There is an underlying presumption that return to the gate may not be practical and, from a risk management perspective, any post-despatch failures can, for the most part, be treated as airborne failures that generally will not reduce permissible certification system redundancies below an acceptable level.
Technically, the QRH becomes the primary airworthiness control document post-despatch. Thus arises our "Practical Gap" because the QRH rarely distinguishes between ground failures and airborne failures - it is, for all intents and purposes, the airworthiness control document that applies from the commencement of "time in service", that is, the commencement of the take-off roll.
So our "Practical Gap" is from disconnecting the tow bar until cleared for take-off where neither the MEL or the QRH practically apply to problems that may arise. The decision about how to resolve the issue is an element of command. Your command judgement is not controlled by the MEL or the QRH: they are considerations that must be weighed up amongst others in terms of the potential consequences of your actions, even if nothing else goes wrong.
And each situation will be different: I may well take a taxiway generator failure airborne on a clear moonlight night, but return to the bridge if it is dark and stormy, the destination involves a serious likelihood of diversion and there is a chance that water ingestion may be the cause.
And when it comes to taking risks, I haven't come across an operator yet that is worth placing myself at unreasonable risk to further their commercial needs!
Stay alive,