@Elac
Nice Post Elac, must have taken alot of thought and effort. You are absolutely correct that this thread will sharpen the mind of AB FBW operators that is for sure.
There is one crucial factor in your post that you have missed, that is the runway was not only wet but slippery. Like thin ice was mentioned. In this case the extra % could be very different from that mentioned in the MEL. Dont forget the aircraft did actually slow down so the brakes must have been working.
The wet + 1/4" gives a landing run of 2600m without GS, which may still be optimistic.
BUT with ground spoilers 1655m. A massive difference of almost 1000 meters and very significant. A little more than the 600'-800' mentioned.
As for the Brakes - this will only be confirmed by the FDR as to how much pressure was getting to the wheels and on first application of Brakes. This of course is regulated by the anti-skid system.
TAM according to the posts here use Manual Brakes(Normally). The CVR which is incomplete makes no reference to an A/B selection. Sorry if I missed it on previous post. Any reference made to the FDR is only speculation at this stage. This is only important as if they were aware they had to use manual brakes then this should happen immediatley on touch down.
In the TW case autobrakes were selected and it took 18 secs for them to realise they were not actuating.
My money is on, the lack of spoilers which played the star role. Without them the aircraft was still producing lift, couple that with a slippery runway equals no braking action.
Jim