I have not read the BEA mentioning the NAV IAS DISCREPANCY ecam msg ... did I miss it ?
CONF:
This is a good question.
From observation, this ECAM message will only appear if there is a 'single source' discrepany between the two
displayed airspeeds. In other words, you're looking at, for example, one PFD at 250K and the other at 200K. One ADR output is erroneous and the message is providing info much in the same manner as the old 'instrument comparators' did. Something's displayed wrong here, you guys check it out.
With the displayed speeds sourced normally from ADR's 1 & 2, an erroneous output from ADR 1
OR ADR 2 (not both) will result in this message (10 second delay). (Conversely, if the problem is with ADR 3 and it is not switched, you won't see this message unless you had a reason to transfer either side to ADR 3.)
Once you get 'multiple' discrepancies (i.e. 2 or 3 ADR's), the message 'downgrades' to the ADR DISAGREE status.
What's interesting is...if this is done in sequence, 1 ADR and corresponding IAS DISCREPANCY, later followed by multiple ADR's and resulting ADR DISAGREE message, the IAS DISCREPANCY message is dropped out of the ECAM string permanently (not recallable), leaving only the ADR DISAGREE actions.
If you have simultaneous ADR problems (within 10 seconds), the ECAM jumps right to ADR DISAGREE & bypasses the IAS DISCREPANCY message completely, which may have been the case here.
With respect to the timing associated with ADR DISAGREE in the report, I recall someone saying in one of the much earlier threads that the times associated with the downlinks were not necessarily the actual times of the message appearance, but I could be wrong about this.