CONF iture asked :Svarin, what’s your take on this ?
I will summarize very quickly here :
At the start of accident sequence, two apparently unrelated faults
PROBE PITOT 1X2/2X3/1X3
WRG:ADIRU1 BUS ADR1-2 TO FCPC2
PROBE FLR is very likely due to icing of probes by high altitude ice crystals.
It triggers a specific 10 seconds ADR checking process by all three PRIMs.Starts 02:10:05.
All three PRIMs work in Alternate 2 for 10 seconds.
WRG FLR affects PRIM2 by cutting it from ADR1 data. My take is this happens right at the start of above mentioned 10 seconds ADR checking process.
At the end of these 10 seconds, each PRIM will either confirm and latch Alternate 2 [B]or revert to Normal law, based on differences between ADR values. This is the purpose of this 10 seconds checking. This happens at 02:10:15.
My take is PRIM2 reverted alone to Normal, while PRIM1 & PRIM3 latched Alternate 2. This is because PRIM2's set of ADR data, being different (only ADR2 & ADR3), would have allowed differences into the 50 kts range that triggers reversion to Normal law.
The sentence "the aircraft was in Alternate 2" makes no sense. The PRIMs compute flight laws, not "the aircraft". All three PRIMs are 99.9999% of the time in full agreement. Not this time.
NAV ADR DISAGREE is CMC stamped 02:12 and ACARS ground-received at 02:12:51, which means it happened on board between 02:11:58 and 02:12:43. Aircraft was downwards fast at that time. Therefore, the ADR DISAGREE condition was not in effect to latch Alternate 2 for all three PRIMs at the start of pitch-up sequence at 02:10:16.
At 02:10:16, the pitch-up sequence and "zoom-climb" happened with (according to my research and "flimsy theory") PRIM1 & PRIM3 in Alternate 2 and PRIM2 in Normal.
If so, this would be a serious system flaw and therefore I disagree.
There’s only
1 PRIM in control and that will be the one which can deliver the highest possible law and in the sequence PRIM 1, 2 & 3
If PRIM 2, in your view, is in control and able to deliver NORMAL LAW this means that PRIM 1 was not able to compute NORMAL LAW protections and doesn’t say anything about the ability of PRIM 3. If PRIM 2 is in control in ALTERNATE LAW this means PRIM 1 and PRIM 3 could not deliver NORMAL LAW and PRIM 1 was also unable to deliver ALTERNATE LAW.
I’m sure if PRIM 2 was in (NORMAL or ALTERNATE) control this had already been mentioned in the BEA update.
ALTERNATE 2 mode is latched, so once it is declared (at the time message F/CTL ALTERNATE LAW appeared on ECAM and PF called it out) there can only be a reset on ground with all hydraulic systems depressurized.
In my view, at that time PRIM 1 was in control, PRIM 2 and 3 couldn’t compute NORMAL LAW either.
Due to the PITOT problem they had all the same ADR information.
PRIM 1 declared ALTERNATE 2 LAW and no PRIM can revert to a higher law anymore even if ADR becomes normal thereafter.