Originally Posted by
Chris Scott
Reviewing the big picture, it does seem strange that Airbus aircraft have latterly been experiencing so many problems resulting from icing of pitot probes, and now AoA probes.
The Thales AA pitot tubes at the root of the problems that led up to AF447 were an optional fit that was only available from the end of the '90s. Prior to that the only units fitted were the Goodrich models that the A330 and 340 were originally certified with. Jet airliners have had problems arising from blocked pitot tubes since at least the early '70s and probably earlier (they were central to the Stony Brook NWA 727 disaster, as well as Birgenair 301's B757). What was new about the problems with the Thales AA model was that because they were individually more susceptible to blockage from ice and supercooled water, the risk of a triple failure - previously considered remote - grew considerably.
It appears that the new AoA vane housing (also available from both Thales and Goodrich) is a new design intended to reduce the risk of the kind of blockage that brought down the Perpignan A320 and caused a single vane to freeze in the case of AF447. As yet, we don't know which model was fitted to the aircraft in this incident, but it appears that the EAD is causing a review of this new design and a fix should be in the works.