A Re-think Required
Retired F4
Nobody's denying your right to comment but the very valid point is that:
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a. An experienced crew wouldn't soldier on into heavy icing conditions without diverting off-track.
b. Because cumuliform cloud (and assoc up/downdrafts) is highly localized, I'd very much doubt that a "downed by heavy icing" scenario would be a player at Flt Lvl 350.
c. From that same pdf file you're quoting comes:
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"1.3.4 High-Level Clouds
High- level clouds, such as cirrus clouds, with their bases above 20,000 ft, are usually composed of ice crystals that will not freeze onto the aeroplane, and so the risk of structural icing is slight when flying at very high levels." But it's not structural icing that we speak of here. It's a compilation over time of supercooled ice crystals inside pitot tubes - in a continuous layer of cloud dense enough that the pitot heaters' heating capacity is being overcome thermally by the super-cold ice-crystals (not a theory, an admitted fact that's now being belatedly addressed by an AD).
d. Because there's no turbulence or structural icing in dense CirroStratus, there'd be nothing on their Wx Radar and no cause for concern whatsoever for the crew about icing. No instrument tells you that the pitots are ALL icing up and crews normally monitor the Fuel synoptic page, not the Engines page. With those non-moving thrust levers of Airbus and crews relying upon their ECAM for engine-related warnings, they'd just not notice that the thrust was increasing incrementally to offset the "system (but not crew) perceived CAS loss" - and causing them to fly perilously fast.
So it's a really nasty set-up for a nasty surprise just as soon as the split between the two sources of static pressure starts becoming so significant that BARO hold is rejected and the autopilot drops out. Pitch-trim state when the autopilot drops out? Another potential ball-of-wax. Where's the THS taking its auto-trim cue from? The increasingly duff CAS? How much (by way of out-of-trim) pitch force was being HELD by the autopilot. Take that a bit further and you might conclude that when the autopilot dropped out the aircraft was trimmed for the HIGHER speed and the nett result was a strong and instant nose-down BUNT. Just imagine them instant apples!! Straight into Mach Tuck - courtesy of the nose-heavy mis-trim? I'd guess so.
Another question might be: "If the baro hold was being corrupted by a false "computed" static pressure, was the aircraft maintaining a genuine FL350 on 1013Hpa?"
Don't know exactly how the ADIRU calculates its static pressures for baro-hold, so can't really comment upon that. But you can be sure that the static pressure component reported by the pitots' ADM's would be increasingly different to the valid one being reported by the uncorrupted static ports, as the pitots became increasingly blocked.
If you disagree, then dismantle the argument with some sort of well-argued counter-proposition or an indication of where the theory fails.
That crew wasn't a made up of fools, just pro-pilots doing a job and likely getting caught out by a very insidious cascade of cumulative error leading to an instantaneous happenstance. I'd guess that any A330/A340 crew would have lost that battle. We owe it to that lost crew to deduce their predicament by utilizing the best tool that's ever likely to now become available - and that's deduction based upon known precedents.