Here's an excerpt from an article in CNN on-line by Kieran Daly:
"An iced-up Pitot tube deprives the pilots and the aircraft's automatic systems of airspeed information, making the aircraft much harder to fly and preventing numerous onboard functions from working properly -- a highly plausible explanation for the string of error messages sent by the aircraft shortly before the crash.
As it happens, an unusually detailed account of what happens in those circumstances has turned up in the form of an internal memo written in French last December by the safety office of the small airline Air Caraibes Atlantique, which suffered the phenomenon twice in quick succession.
They called a meeting with Airbus in which the airline's flight managers pointed out not only what had happened, but also the difficulty of understanding the immediate actions that Airbus recommended pilots should take. I've read it, and it is decidedly confusing.
Now picture the crew of AF447 struggling with that unfamiliar checklist at night, in a cockpit hammered by severe turbulence, possibly lightning, with no airspeed information and numerous warning lights and alarms sounding.
It is difficult to imagine many bigger challenges for a pilot, and anything short of near-perfect execution would have the potential for loss of control.
But the fact remains that this is today speculation."