Since people seem to be posting their full hypotheses, I thought I would have an attempt, as an alternative to grity's fascinating "zoom" idea. Apologies for the length. I also anticipate I am very likely to make mistakes about the aviating side, so stand to be justifiably flamed & hope to be corrected where I deal with those issues.
I am still wondering whether the CB is the initial problem and the pitots were not the precipitating cause, but a very early consequence (and ultimately fatal complicating factor). I've tried to pull together some of the excellent things posted since the beginning of the first thread. Here goes:
Step 1. Aircraft travelling at about M0.82, at FL350 on its planned track.
Step 2. They don't see storm on radar (for whatever reason) or for some reason try to penetrate it (eg including penetrating the smaller front system and not seeing the big one behind it). Crew is otherwise alert - as evidenced by eg the failed SELCAL calls just before.
Step 3. Tim Vasquez's graph shows that 2:10 corresponds with a position in the middle of the larger CB assuming more or less continuation of direction of flight, which is why I choose it as the initiating factor.
Step 4. The first encounter is a severe up or downdraft - aircraft rises or drops very suddenly and
very significantly due to air movement or change in air characteristics or both. Given the overall high loss of altitude with short net horizontal distance, I assume a strong downward motion.
Step 5. We get the host of messages, AP off, ATHR off, windshear detection off, alternate law and TCAS fault. Also the flag on cpt pfd spd limit and on f/o pfd spd limit, with the LKP (higher priority message) interposed between them. This is where I am likely to be totally wrong, and stand to be corrected, but could this all be a consequence of a sudden massive altitude change due to the storm?
Note that BEA said of the TCAS fault:
"Amongst the possible external failures, only one is compatible with the CFR received. This is a monitoring process internal to the TCAS which applies to the standard altitude parameter. The latter is received from the active transponder (it can thus be the altitude elaborated from ADR 1 or 2) and is submitted to a “credibility” test. In actual fact the TCAS elaborates an altitude prediction that it compares permanently with the altitude received. When these two parameters move too far apart, it stops operating and generates this ECAM message.
Step 6. Assume that still at around 2:10, we
then get pitot icing. (eg encounter large amounts of supercooled water/ice etc). This in turn causes the associated MAINTENANCE STATUS EFCS 2, MAINTENANCE STATUS EFCS 1, Pitot and "ADIRU1 BUS ADR1-2 TO FCPC2" fault (that svarin noted some time back ) messages. We also get a rudder travel limit fault at this time.
BEA said of the ADIRU message (report 2, p37):
It is possible to explain this message by the rejection of ADR 1 by FCPC 2. It is correlated with the MAINTENANCE STATUS EFCS 1 and EFCS 2 messages.
The pitot message appears to indicate a
drop in calculated speed. See report 1:
FCPCs (or PRIMs) 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, because the prior rejection of an ADR would have generated a class 2 fault message and there would therefore have been an asterisk in front of the source. In this case, the “polled” value is the median value.
I seem to recall a suggestion that the rudder limiter message is also a result of unreliable airspeed (ie the sudden drop), but cannot find justification now. As MM43 just noted, BEA wrote that the examination of the actual assembly from the recovered VS showed it was at "7.9° +/- 0.1°. As an example, at FL350, this travel is obtained for Mach 0.8 +/- 0.004, corresponding to a CAS of 272 +/- 2 kt." At this point the aircraft, at least, thinks it is around kcas 272 [strikethrough]M0.80[/strikethrough].
[So at this point -- the a/c has dropped suddenly, and IAS has dropped suddenly, and AP/ATHR are off, plus we are in alt law. Now the pitot failures have started to affect everything else. Pilots also confronted by a bunch of unusual messages all at once?]
Step 7. Moving into 2:11, we then get then get a whole host of failures consequent on the icing - Flag on CPT PFD FPV and F/O PFD FPV. Then speed or mach function and and ADIRU2 fault.
BEA states that the speed or mach function fault could have meant CAS was above or below the relevant limits -- but which of these is the case is not captured on this aircraft (report 1, p53). Given we had a drop in airspeed before, hypothesise that it dropped below the lowest limit to trigger the message.
BEA says of the ADIRU2 fault (report 2, p 38):
This message was generated by IR 2. For an ADIRU of this standard, it means that the IR considered that the three ADRs were invalid, that is to say that at least one of the three parameters was invalid (SSM status not NO) amongst pressure altitude, barometric vertical speed and true airspeed. As soon as the third ADR is rejected, the IR generates a message pointing to its ADIRU. If one of the IRs considers the three ADRs as being invalid, this must also be the case for the other IRs. It is therefore logical that, in parallel with this ADIRU 2 message generated by IR 2, an ADIRU 1 message was generated by IR 1 and an ADIRU 3 message by IR 3, which would explain the presence of the latter amongst the identifiers.
The fact that EFCS1 was present amongst the identifiers preceded by an asterisk indicates that EFCS1 had at least generated one class 2 message, perhaps followed by a class 1 message. There are too few elements available to determine precisely what the presence of EFCS1 amongst the identifiers means. Nevertheless, it is possible to state that it concerns a rejection of ADR by at least two PRIMs. It has not been possible at this stage to understand why EFCS2, the clone of EFCS1, is not an identifier.
Step 8. At this point, indicated airspeed is way off -- probably much too low. It is dark, middle of thunderstorm, turbulent, possibly raining heavily. Aircraft is in alt law, no AP and the computers are failing. The crew has no AoA indication in the cockpit. What would you then do? Nose down either unintentionally due to disorientation, or unintentionally as a result of turbulence or intentionally from a desire to increase speed if they believe the speed has dropped? Or nose up, again either mistakenly, from turbulence or on purpose? Either leading to fast steep dive or nose up deep stall?
Step 9. At 2:12 we have Nav ADR disagree, which is the only message time stamped 2:12. According to BEA (Report 1, p 50) "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." There are no other messages time stamped 2:12. Pilots are attempting recovery? Attempting to hold prior speed and AoA?
Step 10. We then enter the period 2:13:14 to 2:13:45 where no ACARS are received. It seems that aircraft orientation prevents ACARS messages being transmitted. (Control has now been fully lost? Possibly severe roll, or spiral? Or a hard dive, or very high AoA stall where the body of the aircraft itself blocks the ACARs transmissions from reaching the satellite?) In any of these cases, losing altitude very fast, horizontal speed decayed (if nose up) or a minimal component of overall velocity vector (if nose down). PRIM1 and PRIM2 faults, and FMGEC faults are generated but are saved up until ACARS can resume. (Aircraft so far out of normal envelope that the computers finally give up the ghost?)
Step 11. When ACARS transmissions resume, the PRIM1 and PRIM2 faults are transmitted. Then the interposed ADR2 maintenance status message (time stamped 214) then the FMGEC message (time stamped 2:13), then finally the cabin altitude advisory (time stamped 2:14). Aircraft is relatively low now. High vertical speed. Little horizontal speed.
Step 12. ACARS messages stop. Note that one reason BEA gave is "loss of electrical power supply: this would imply the simultaneous loss of the two main sources of electrical power generation." Finally, the flame out? Might this suggest high AoA deep stall (though why would they not have flamed out earlier if this was the case) or consequence of steep dive or during a partial recovery from steep dive? In any event, it seems no relight succeeds.
Step 13.Within a minute or so (perhaps longer), the aircraft has hit the water. At this point, aircraft is at level orientation (wings level, nose slightly up, the famous "en ligne de vol") - possibly partial recovery but with not enough altitude left?