Why were they ignoring the Papi and why were they slightly east of the centre line?
I don't know that they were ignoring the PAPI, or if they were, why they were.
Ms Benson's house, where they first struck trees is almost precisely on the extended runway center line.
I am not sure what you mean by published altitude.
The MDA. If they hadn't descended below MDA, they wouldn't have hit anything. Obviously, you have to do that to land. But if you *don't* descend below MDA until you are on the PAPI with 2 white and 2 red, you won't hit anything after you leave MDA.
That of course assumes:
1) No gross altimetry errors
2) The PAPI was working correctly as commissioned.
As far as I know, 1 and 2 haven't been ruled out, but if both are true, then in order to arrive where they did, they must have descended below MDA before being established on the PAPI g/s.
Why, we can only speculate at this point.
As far as the terrain warning, EGPWS will inhibit the terrain warning within a certain distance of a published runway. I don't know the specific parameters of thier system, but they may have been within that distance where the system doesn't give terrain warning.