backseatjock Article from today's New York Times, which links to above threads.
Investigators are pursuing a theory that excessive air speed -- potentially spurred by ice building up on electronic airspeed sensors -- contributed to the ocean crash of an Air France Airbus A330 amid heavy storms Monday, according to two industry officials familiar with the details............
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If the tubes iced up, the pilots could have quickly seen sharp and rapid drops in their airspeed indicators, according to industry officials.
I'm not sure why anyone has to presuppose iced-up pitot tubes or that the cockpit airpeed indications were erroneous. Sharp and rapid decreases or increases in airspeed while within or above a CB that produces violent atmospheric shearing and/or updrafts/downdrafts are going to occur. All the cockpit indications may have been absolutely correct and shown the true picture of the situation if they were in one of the magnitude the weather picture indicates they may have been; that any aircraft's capablity to counter such very real and extremely dynamic atmospheric forces may not be enough (especially at high altitude and heavy weight where aerodynamic and performance are seriously degraded compared to even 10,000 feet lower).
To me the most telling and glaring ACARS message is the first one...Autopilot Disengament....not the flurry of messages that come a few minutes later. Something caused this. The autopilot's inability to hold altitude or being buffeted past it's pitch or roll limits will cause the AP to disengage. Given the context of where they were and the pilot's own message to his company a few minutes prior regarding turbulence, this has to be considered and from this moment the pilots were hand-flying with various flight control limiting protections against aerodymamic excesses removed.
If an aircraft also enters into an extreme updraft (such as those found inside
or above a rapidly developing CB) the Autothrottle would begin to close when the airspeed rapidly rose, or the pilots might disengage it if the ATs aren't reacting as swiftly as the pilots need or want.
And if, while in an extreme updraft, the A/P disengages due to the inability to hold the selected altitude and the pilots do what we're normally trained and told to do in that abnormal situation...attempt to maintain pitch and wings level in order not to exceed AOA and load factor limits and control the speed if with thrust while letting the aircraft ride the updraft to a higher altitude (or to a lower one in the case of a downdraft)...that aircraft is going up.
But if the aircraft is already flying at it's maximum enroute altitude near the top of it's operating envelope for that loaded weight when an extreme updraft encounter begins, it could suddenly find itself higher than it should be...a thousand feet higher?...higher still?.... and therefore in a very perilous situation when it exits the updraft. If it's still being buffeted while at that higher altitude, engines spooled back due to the A/T or pilot's prior attempt to counter the indicated (and very real, not "erroneous") acceleration towards overspeed due to the shear accompanying the updraft, but now suddenly the airspeed is rapidly decaying and excess available engine thrust to stop and reverse decaying trend even more limited becaue of altitude, the situation is downright hairy.
Did this happen to this particular flight? Only the FDR will tell. But what can be said is that
it's a very real and possible scenario for any heavily-loaded aircraft near to top of it's current operating envelope if it enters or flies just above a quickly developing CB.
Recovering or attempting to recover from this scenario while descending (and you MUST descend to recover) through the severe or extreme conditions inside or around the CB itself could easily result in a cascade of failures and/or failures of electronic self-monitors and sensors within the aircraft, especially if one or more engines flame out.
That "aerodynamics lost" situation is a KNOWN and ALWAYS-present threat in high-altitude flying that we mitigate through choice of crusing altitudes, routes, and actions
to get ourselves away from near the edge of the performance envelope if conditions change or develop that could put us outside what was previously comfortable. It's present even with no thunderstorms within 1000 miles. If you pass into or are pushed by extreme and sudden atmospheric forces (like are found in or around CBs) into an aerodynamically unviable situation/jet upset, very few air data indications in the cockpit will be reading correctly even on a clear, sunny day after that occurs.
There's no need to pre-suppose any pitot or probe heat failures or erroneous readings as a cause for the worst happening, and icing severe enough to overcome working pitot heat would normally be found at lower levels (which would of course hamper recovery, assuming other essential structures and powerplants are still working).
And similarily, there's no need to presume a worst-possible-moment, made-for-a-disaster movie script lightning strike that coincidentally knocks out the one component you really need in a CB-avoidance situation...the radar. What can't be seen can't be avoided, and radar still has limitations even while in good working order, especially when it comes to painting the kind of young, developing cell that creates severe-to-extreme updrafts within itself up to thousands of feet above it's visible (by eye or radar) top.
Once again, mitigating the chance of encountering airborne threats is what we do, but the smaller the eye of the needle you thread while picking your way through CBs...especially in a very dynamic steady-state or developing area...the smaller the chance of mitigating it at all. The small or "soft-looking" as-seen-on-radar area you believe is the best route can quickly close up, especially if you're also seeking to avoid being directly over developing cells where the worst turb can be found. And at FL350 and heavy, any pilot should be avoiding that particular spot for that reason, because if a cell is buildng at 10,000 fpm it's a trap for envelopement. Get closed-in, and it's guaranteed your world is going to be rocked, so perhaps the only way to mitigate the threat is to quit worrying about deviating around individual cells and take the 200 or 300-mile deviation around the whole, cursed area.
To me, combined with the pilot's earlier message, the A/P disengaging first with no coinciding source/power failure messages is the biggest red flag of all. What are the possible reasons for it to do so while it's still powered and functioning? Just because it's not controlling the airplane anymore doesn't mean it isn't functioning, or that it only thinks it's being asked to do something it can't due to erroneous Air Data, iced-up sensor input. It's disengament was probably the exact thing it was designed to do under certain conditions, and unfortunately there's the very real possibility that atmospheric conditions outside the aircraft could have been dictating the show into an entenable position from that point on, or perhaps it was even at that point already.
I truly believe many are overcomplicating this. Not every aircraft accident is an overly-complicated series of many technical-issue, swiss-cheese holes. The Laws of Aerodynamics represent one, rather large one when you're mixing it with CBs.