I heard it was pitot icing which isn't supposed to happen on heated
pitots which all icing condition certified aircraft should have.
Take away that info gather by the pitots and you disable the
aircraft's ability to process flight dynamics. Pitot readings
indicated a lower than normal airspeed, the engines throttle up
and the aircraft then flies too fast for the turbulent conditions
causing a catastrophic failure of the airframe. Decompression occurs
and the airframe breaks apart at FL 330.



Yeah. Lots of interesting stuff coming out now. From today's newspaper --

" ..... investigators said that the Airbus's pilots had no idea how fast
they were flying after sensors iced up and the computer went haywire. The
computer sent 24 error messages and was flying without autopilot or cruise
control. ..... it was not clear whether the autopilot had been switched
off, or had stopped working. Mets said the jet flew into a freak storm with
100mph updraughts that sucked up seawater that quickly froze. .....
said the lack of speed readings meant the pilots would have stalled or used
more power than the jet could take."

Taking N.Cook's point about the Pitot being only one input. This is true,
with there being secondary inputs from the INS and from GPS. However, as the
Pitot data is fundamentally 'mechanical', it is considered the data of
primary reliability. Presumably, the fact that it was (possibly) giving
erroneous readings, should have led to the data from the other two sources
being taken into account, and a two out of three decision made on that
basis, but there may be a software conflict situation arising out of that. I
don't know if that aircraft has one or two tubes, but if it has two, and
they were both icing and giving the same wrong reading, that may have been
enough to screw the decision making process. My flying chum says that as
well as ramping the engines up, if the flight control systems decide that
the airspeed is still not going up, then it may well put the nose down as
well in an effort to increase the speed. Then you are in a full power dive.

The ACARS error messages are purely for advance maintenance purposes, and
are simplistic in that if the pilot switches a system off - such as the
autopilot or the auto cruise control - this will immediately trigger exactly
the same 'error' message as if the system had failed on its own. There is no
distinction between a failure and a deliberate disconnect. Either way, it is
an 'error'. The bad thing is though, that if the system is then switched
back on (or recovers from a temporary fault), this does not trigger a
different message to say it's back on. It is just an error that has now gone
away again.

Another interesting point is that the aircraft took on every last ounce of
fuel that it could, before leaving Rio. Not so much that it was overloaded
out of spec, but much more than it would have needed for the flight with
divert margin. So this might mean that the pilot was aware of the massive
storm on his proposed routing, and was covering for the possibility of
having to go around it. However, all of this extra fuel meant that he could
not attain his filed flightplan cruise altitude of FL370, and was instead,
at a radio approved FL350.

If it does turn out to be down to Pitot icing, and this was a known problem,
I wonder if a charge of corporate culpability will be levelled at Airbus ?

That one that you mentioned where the tail fell off, I seem to recall that
was due to a stress fracture in the composite which was repaired with a
horseshoe of ally rivetted on over it. This is a valid repair technique for
an ally skin fracture, but not for composite. I believe that there are no
approved techniques for repairing this kind of problem, in this kind of
material. Apparently the aircraft that has just gone down, was involved in a
ground collision a couple of years back, when its wing hit the tail of
another aircraft, doing that tail serious damage. I wonder if any unseen
latent damage was done to the Airbus's wing, that then failed in the
turbulence / excess power conditions ?

Arfa