Hi,
Originally Posted by Hyperveloce
thinking to this last ACARS at 02:14Z, we can bear in mind that all the past Pitot freezing events duration was less than 4 mn (typically 3mn): even if the static ports were compromised during the cruise phase at high altitude at 02:10Z (during these past events, it induced a slight barometric altitude bias: a few 100ft), after more than 4 mn and probably, in the AF447 case, a large loss of altitude (external temp. increase), isn't it probable that the air data (ADR) had recovered/de-iced ? beside the BEA reports have raised the possibility that the PRIM were manually reset at 02:13Z (to explain ACARS that were not seen during the other past Pitot freezing events): if true, this could only have happened because the air data was back at 02:13, prompting the crew to try to regain the normal law, don't you think ?
Well, there is no rule saying that, because previous documented freezing events at such high altitude lasted from few seconds to 2 mn, this one would be over after 3 mn. Also, none of the previous events caused an aircraft to crash. Going lower may in fact add much more to the problem rather than resolving it as we might suppose that they were flying above thunderstorms. In fact, much more water particules would be encountered below AF447 actual cruise level before going out of the "freezing zone".
The only reason (beside other problems) why they would have to initiate a descent is that they couldn't climb above this level while turbulences would make their current flying altitude dangerous.
Furthermore, going back to "Normal Law" was certainly not an option as they would have to land first before it could be restored. Once ALT2 is triggered by such faults, they would be struck into this mode until landing and maintenance performed on the Air Data systems.
S~
Olivier