Pitots may have worked properly, ADU error checking may have precipitated the event.
I have been silent for 12 months but would now like to raise the following for discussion.
1) The BEA#2 report indicates a sudden increase in speed inconsistency reports (7 times the frequency) from a point about 2 months before the peak in oil prices. Could this coincide with a renewed emphasis on flight plan optimisation with respect to fuel??
2) Speed indication of Mach by pitots can be over-estimated in a Cb and TAT will over-estimate SAT when using the over-estimated M.
Standard atmospheric air (mostly diatomic) has a Cp/Cv ratio referred to as G (gamma). Normally the low humidity, low pressure and low temp air at cruise level means G is relatively constant. Add abnormal % of water (triatomic) and G is no longer constant but decreases (BEA#2 'strong condensation' pg69).
The air density value is required for the pitot to measure air speed but M can be calculated from pitot results if G is assumed. As G decreases, M is overestimated by the pitots. This M value is used to correct static pressure giving an altitude calculation variation (error) even if the altitude has not altered and there has only been a change in G. This M is used to calculate SAT from TAT. SAT is also overestimated.
On a sudden change in Ps (altitude) calculation due to incorrect M, the TCAS (BEA#2 pg 35) ACARS would appear if Ps fails the 'credibility test' @2:10.
The IR may also reject the ADU sudden changes in calculated data (due to the variation in G), hence the ADIRU fault (2:11).
It seems possible that a sudden change in the air property (G) due to the Cb could start the cascading faults shown in ACARS due to internal error checking. This then leads to the A/P and A/THRUST disconnecting although the A/C may not have altered its velocity or altitude.
I don't recall this being raised previously. My apologies if it was. My concern is that AF447 may be somewhat repeatable if 'heat upgraded' pitots are installed as this does not alter the above, albeit rare, scenario.
thanks. Ian