BOAC:
I'm sure I asked this before, but cannot now recall if was answered/deleted whatever.
I hear 'undercurrents' that are talking about loss of attitude data. There is nothing specific on anything posted here from the ACARS list to suggest that. The question (again?) is would the loss of the AD part of an ADIRU render the IRU part unusable/unavailable either de facto or due to software intervention?
BOAC:
Maybe the answer to your question is
here.