1 – FACT : a careful reading of the first 3 pages from the (probably leaked) ACA report (available at
Eurocockpit - Accueil, direct link is
http://www.eurocockpit.com/docs/ACA.pdf). Everything is in these first 3 pages, although the rest is well worth reading too. In short, one of two incidents on A330s with loss/discrepancy in all airspeed indications.
2 - HYPOTHESIS : from the available sequence of ACARS messages, let us postulate that the pilots in AF447
faced the same situation as did the ACA flights mentioned above.
3 - FACT : in the last paragraph on page 3 of said ACA report, the ACA flight Pilot Flying deliberately ignored all STALL warnings,
contrary to what is requested by TECHNICAL RECOMMENDATIONS from the UNRELIABLE SPEED INDICATION C/L.
4 - HYPOTHESIS : following the same C/L, facing the same situation caused by the same conditions, let us postulate that the AF447 pilots
do indeed heed the STALL warnings, as requested by C/L. In so doing, while having a mental picture of trying to fly away from a low speed stall condition, they actually fly towards a high speed buffet and beyond.
The ACA incident lasted 1 min 26 sec. It is not unreasonable to assume an approximately 4 minutes duration for the AF flight, from 0210Z to 0214Z.
From the initial condition : loss of all 3 airspeed indications, the ACARS messages pertaining to flight controls and other instrument failures are aggravating circumstances, but they are not necessary to explain the scenario at point 4 above.
Another report that can be found on the internet, regarding one AF 908 CDG TNR, describes a very similar situation. Again, the pilots disregarded the STALL warnings.
I remain ignorant of the actual circumstances of the AF447 accident. The reasoning above is, by necessity, a conjecture. It is however founded on very simple hypotheses, making it a good candidate to confront a sharp Occam's razor.
I find it necessary to point out the fact in item 3 above, regarding STALL warnings and how the C/L deals with these.