Rational between ACARS messages.
augustusjeremy, re #3694
It is not just the 'IR2 fault' message that questions the 'blocked pitot theory'.
As the BEA report reiterates, the ACARS messages are maintenance messages for the ground crew, not warnings to the flight crew. A maintenance message that is generated by a system's BITE should be due to that system's BITE detecting an internal fault:-
1 NAV TCAS FAULT Message.
As indicated in the BEA report (page 50) the cause is unclear. I suspect that the most vital parameter derived by TCAS is the relative velocity with respect to other aircraft. As well as a BITE check on max and min, I would expect the rate of change of such a vital parameter to be checked. A rate of change of more than about 20 knots per second for say ten samples might be considered as out of spec and hence warrant a maintenance fault message.
2 ADR Fault.
It is not clear as to the level of inconsistency between the three ADRs; the statements within the BEA report seem to conflict. On page 50 regarding NAV ADR DISAGREE message, “Meaning: This message indicates that the EFCSs have rejected an ADR, and then identified an inconsistency between the two remaining ADRs on one of the monitored parameters.”, but on page 51 regarding the PROBE-PITOT message, “...triggered one of the speed monitoring processes: they have detected a decrease of more than 30 kt in one second of the 'polled' speed value. The three ADRs were considered valid by the EFCS2 at the time the monitoring was triggered... “.
3 ISIS SPEED OR MACH FUNCTION
Presumably this could due to the same cause as for the ADR Fault; what a shame that the CMC does not send the flag status, just a single character representing 'flags code' would give so much information at so little cost! Or if the info in post #1442 is correct (but #1757 is not), this could be a problem with gyro derived direction.