AF447 Thread No. 3

[PEI_3721]

The aircraft encountered unusual weather conditions (not in a Cb) which resulted in erroneous airspeed.
The crew instruments used this data (thus the abnormal indications), and other systems including the flight control computers, which interpreted some values as invalid (out of tolerance), and thus reverted to an alternative control law.

The FDR recorded the erroneous values of airspeed, which were not the actual aircraft speed, nor necessarily even after the ‘icing’ encounter with apparently ‘real’ airspeed values – ice blockage still clearing etc.
It is assumed that these same erroneous data were displayed on the PFD / ISIS, if at all, due to out of tolerance blanking.

In alternate law, the aircraft commenced a climb; probably a combination of trimmed state – residual A/P trim before disconnect and ‘inadvertent’ crew input – lack of control force feedback.
Question; does the THS automatically follow up a nose up command in alternate law?

In alternate law, there appears to be some high speed protection. Thus even with increasing AOA (and subsequent stall warning), if the ‘sensed’ erroneous airspeed was high ‘over-speed’ (“sharp rise in ‘recorded’ airspeed 215 kts”), then an automatic nose up command would be provided to reduce speed. ( In the small print / notes – alternate law.)
Question; does the THS automatically follow up in this condition?

A change in yaw / roll control law and/or loss of yaw damping in abnormal alternate law could have contributed to the apparent roll control activity. Not discounting turbulence.

The aircraft decelerated in the climb, approaching the stall, but not necessarily stalling immediately (note nose down pitch control inputs, 7000 ft/min – 700 ft/min). The crew, without airspeed indication (or at least viable display values), experienced conflicting information; stall warning from the AOA vanes, but nose up movement (and trim?) from a potential over-speed condition (erroneous airspeed – as above).

Nose down control corrective action had minimum effect due to nose up THS position (and TOGA contribution). The aircraft apparently stalled with nose up trim, but subsequently, the crew at times had apparently ‘reasonable’ airspeed indications and no stall warning (AOA inhibited at very low speed).

The aircraft remained stalled, the crew had conflicting / minimum information, the trim remained nose up, and the crew had no control force feedback of the aircraft’s trimmed state.

Question; does the stall recovery action, or any other low speed flight, require the crew to check the trim (THS) position?

Question: at any time in this scenario, did the display of aircraft attitude fail?