Extract from the ATSB report on A330 VH-EBA incident (28 October 2009) – Flight Guidance system description:
“Each flight director automatically re-engaged when its associated FMGEC detected that at least two ADR values were again valid and consistent.”
Note: ATSB always uses the past tense.
If this is correct, according to the BEA update on AF447, the FDs could have been available from 02:11:06 (when the IAS was restored on the ISIS) to a few seconds after 02:11:40 (when all speeds became invalid).
In what mode would the FDs “re-engage”?
Did you ever observe FD hypnosis?
For those interested, there is a hint about HS / Elevator relative efficiency in the A330 FCOM3 under F/CTL STAB CTL FAULT emergency C/L:
“If trim is locked above 8 degrees UP, pitch down authority may be insufficient for speed above 180 knots”