A320 engines out DITCHABILITY?
 

FBW /APU starting and controllability?
.
.
When the A320 went into the Hudson River, the Captain deviated from the checklist cadence and quite appropriately fired up the APU, more or less immediately after the birds hit.

This action kept electricals (and hydraulics?) and retained(?) the FBW mode as NORMAL Law (????).

What if he hadn't started the APU? Would sufficient busses have been powered and would battery power for the 5 min flight have been enough? Would the crew have had their full FBW or have been reverted to a lesser law?

The inference, albeit a weak allusion, from the NTSB's Report was that it may well have been a completely different outcome if Capt Sully hadn't promptly kick-started the APU. As it was, he had significant problems maintaining the desired/appropriate glide speed and the flare-speed (and thus the touchdown attitude) was non-optimal. Why was that?

But if the APU hadn't been started, the degree of controllability that led to a "sufficient" flare (although not optimal - NTSB Report) and subsequent benign ditching might well have been characterised as a crash.... with a significant loss of life due to a greater loss of airframe integrity.

Your thoughts? and some supporting A320 relevant facts?

You make conclusions based on data which may not be true, so it is hard to say.

NTSB has a public docket with large amount of reading material on website, perhaps some answers can be found there.

I heard the tape where FO says "starting APU", but was the (auto)start sequence completed before the impact at all?

The A320 with dual engine failure (full, unlike Hudson) and emergency electric only retains Alternate law FCS mode. To pilot, this is identical to Normal law except the FBW protections are removed.

Hydraulic pressure on a flamed out engine is available down to about 220 kt IAS, again, Hudson was landing significantly slower than that but any thrust on at least one side should keep both engine driven hyd systems available (via PTU).

Yours,
FD (the un-real)