Because it was switched on and it worked.

The larger, underlying question most of us have latched onto is the overuse of MELs to keep an under maintained fleet operating.

Indeed

The captain's swift and thoughtful action in immediately activating the APU also contributed to the successful ditching because the APU allowed the fly-by-wire system to remain in Normal Law. Without the APU, the aircraft would not have descended with the flight envelope and stall protections that Normal Law afforded. These protec-tions proved especially crucial because the aircraft entered al-pha-protection during the final approach, and the system may have kept the plane above the stall speed during the last 150 feet of the descent.

Got any ideas?

All kudos to Sully and his colleague by the way. Without the APU the aircraft would have flown in direct law, (just like a 737). Airbus aircraft land in direct law quite regularly after some in-flight computer failure so I’m sure Sully would have been able to ditch without a working APU. The argument that the accident report tries to make is a bit of a circle reduction. Yes the APU allowed normal law to protect the aircraft from stalling, but without the APU, Sully would have flown the aircraft in direct law, respecting the stall warning like in a conventional aircraft. He could have arguable made a more controlled ditching in stead of (unknowingly!) pulling so far back fully on the side stick that the computers had to take over to safe the aircraft from a stall over the Hudson.

The only area where the APU might have been critical is if an engine in-flight restart would have been possible. Which was not.

So more to the point, did the FAA change any MMEL after this incident regarding serviceable APU? Was there a need?

Everything on the MEL has a time limit associated with it (3 days and 10 days being the most common) - in most cases it can be extended, but just once (so figure 6 days and 20 days), at which time the aircraft is effectively AOG until the defect is fixed.
The intent - as Icarus noted - is that, during that time period, the aircraft will overnight at a maintenance base where the defect can be corrected.

Thanks for the refresher…I am intimately familiar with how an MEL works. The intent may be as you say but the reality is far less purist. The sheer number of aircraft carrying deferred items departing SYD, MEL, BNE etc every morning that also left yesterday morning and the morning before that, and the morning before that is higher now than ever before. As I said, under maintained aircraft being under maintained out of a deference to profit.

The new uniform should fix things though…

Yeah sorry I don't buy into that. Part of this job is standing up for yourself and having some balls to say no sometimes.
I have politely expressed concern at multiple MELs affecting different systems that a captain was happy to accept. Told him I respected his decision as the PIC but I wouldn't be joining him.
Its not something I'd ever do lightly. But very occasionally, it is required. It's not nice nor is it easy but that's why you are there.

Like everything else in airlines whenever there is a limit for something e.g. MEL,FD, FOD, there is now a target. whatever the intent was for a limitation has long been discarded and a binary choice has now been presented. That choice is "are you legal, yes or no?". Too many PIC's have been kowtowed into following the company line but if they understood their legal responsibilities then they would realise that standing firm will not get you fired. As clearice stated an F/O has to also stand firm if they believe the situation is compromised. The only way you get to be a captain that stands up to the company is to be an F/O that is prepared to do the same.

I don’t hold a lot of faith in the ‘legal’ argument as so-called aviation law and what we think is legal can be weak in court.

It would be interesting to actually see what position we are in legally if we refused a MEL then got fired or sued how all that stacks up. The problem is Pilots aren’t subject matter experts so on what basis are we saying something is unsafe? How are you going to argue against Company expert witnesses endorsing the MEL?

I know of too many examples of what was actually safe or the correct decision wasn’t legally ok.

There is a line in the pre-amble that gives the PIC authority as to accept an MEL item or not. End of discussion.

Absolutely correct! Also, we are SMEs on our aircraft type, the endorsement process sees to that.

Sure I am aware of that but where does that stand legally though if it all gets nasty? Those in the industry take the preamble as being the end of the matter, the law may not see it that way.

This will be one of the most under-appreciated posts of 2025.

The bigger question is where is the regulator in all of this?
Clearly they are satisfied with the health and maintenance of the fleets across airlines, cough cough, across Australia.
i mean why were some of the Ansett fleet grounded again in history gone past?
The sh);t is hitting the fan and there appears to be silence from them.

Let's be honest, apart from some CASA tokenism wielding of the big stick at small issues, the Q group is its own self regulator and CASA does what it's told. You only have to look at the fatigue rules to see that.

All of the relevant regulations, the act, and company operations manuals give the PIC final authority on almost everything. They have to as the PIC has final responsibilty for the safety of the flight. With the responsibilty comes the authority.

The company document suite, in its entirety is legally binding. They will hang you with any and all of the applicable document if you ever fvck up. Neither they nor you and I can cherry pick. The preamble is sacrosanct. We shouldn’t be accepting any MEL other than to return to a maintenance base, even then you’d need to be able to explain to a judge why you chose to accept the MEL if you were ever unfortunate enough to be fronting a board of inquiry.

Just for sh!ts-n-gigs, count how many times you hear the word ‘safety’ the next time you pax anywhere. You would swear they believed it.

Agreed.
And if the Captain says we are not going, then that’s it. Game over. End of story.

Flown buses with the APU completely removed because I could. Was it unsafe? No. Was it legal? Yes. Was it efficient? Yes. Would I be having ****ty day IF I lost both engines. Yes. Did that bother me? No. Did I get the job done and was the airline / pax happy? Yes. Did I have faith that the appropriate risk assessment was performed by the manufacture when constructing the MMEL? Yes.