Machinbird;
It is probably highly relevant that AF447 was lost in an active area along the ITCZ, but whether the relevance is pitot icing or turbulence or both or even some other factor is unknown at this time. We can only wonder why they did not see the necessity of altering course as aircraft in front of and behind them did in the ITCZ portion of their routes.
The above is a good
précis of the conundrum we are left with.
We know that AF447 tried 3 times to log on to DAKAR ADS-CPDLC but was rejected due to DAKAR not holding a flight plan - only a virtual one. The last time was at 0200z (DAKAR recorded 0201z) and I suspect that some discussion then took place between both pilots as to how to sort the problem. This distraction (by both) could well have resulted in failure to see anything significant on the WX radar right ahead. At this stage the radar tilt would need to be max down for them to see the Cb cell that was rising at 4,000ft/min right ahead. A few seconds at the most was all that it took for the latent heat of the super-cooled water vapour in the Cb the a/c penetrated at about 0209z, to condense and freeze over the pitot tube ports.
The GS over the period from 0200z to 0210z was 463KT, a reduction of only 1KT from the previous 10 minute period, and I suspect that the a/c had been proceeding in light to moderate chop. However, penetration into an active Cb cell took place shortly before 02:09:30z and the a/c probably pitched up violently and rolled to port as all hell started to break out in the cockpit.
I would go as far as stating that M0.82 was being maintained, though CAS dropped slightly in the chop, and was effectively recorded at M0.80 (272 +/-2 KCAS) by the RTLU as ADRs disagree, reversion to Alternate Law and both A/P and A/THR disconnecting. The 3NM deviation west of track occurred after the reversion to Alternate Law.
Distraction is not a great way to commence recovery from an upset.
A problem I have with the above scenario, is a "chicken & egg" one. Did the ADRs disagree due to Pitot induced UAS due to icing, or side-slip/yaw errors from an external physically induced upset?
No, I doubt if control loop oscillations, PIO or otherwise played any part in what took place. But why and how an otherwise undamaged aircraft (to the best of our knowledge) was delivered to the sea surface is the real conundrum.
NeoFit;
Was there anybody alive in the aircraft before 02:00z ?
The following ACARS messages are relevant:-
2:11:00 WRN/WN0906010210 228300106FLAG ON CAPT PFD FD
2:11:15 WRN/WN0906010210 228301106FLAG ON F/O PFD FD
- which indicate that those pages were selected by the crew.
The reason for the outcome lies deep below the Equatorial North Atlantic.