In the last day the media slightly sensationalised the diversion of QF568 (the 2355 hours Friday 13 April PER - SYD redeye) to MEL due, apparently, to airconditioning system problems.
Flyerqf asked this in the QF delays thread but it wasn't answered: from the flight path, it looks as if there may have been problems prior to the flight being anywhere near ADL. Was the decision to divert to MEL not ADL driven by the lack of staff in ADL early in the morning (say at 0500) due to the curfew, or some other reason?
When aircon fails, does it tend to be a complex job for the mechanics? Fiddly?
As at 1100 hours on Sunday 15, the affected aircraft, A333 VH-QPF looks still to be inoperable in MEL, presumably under repair.
So, I gather that the gist of your question, is why the aircraft went to Melbourne and not Adelaide.
If you had an emergency, then the curfew at Adelaide does not apply. But, nothing actually forces you to land at any particular location, especially if all engines are operating.
There are a number of reasons that the packs might decide to shut themselves down. If they do, the cabin pressure bleeds down, but not at anything like the rate of a rapid depressurisation. It is possible in some cases to get the aircraft below 14,000' before the cabin rises above it, which means that you won't have to deploy the oxygen masks.
It may also be possible to restart/reset a pack or system that has shut itself down. If you could then you'd be able to climb again, although the fuel burn could well still force a diversion.
In this case the aircraft is at 17,000', which is an unusual level. The depressurisation model is for 14,000' until depletion of oxygen, and then 10,000. FL170 isn't part of that profile.
My guess (and that's all it is), would be that during the descent, the oxygen was tripped. It is generated oxygen, which means that it cannot be shut off, and has a life of around 20 minutes. At some point, the initial problem was resolved. But, the aircraft no longer has supplementary oxygen available, so it would be altitude limited, and I suspect that's where the FL170 came in.
There is no longer an emergency, and Melbourne is within reach, so there is no real reason to land at Adelaide.
A guess, but it makes some sense.