Pitch trim
As I've read the report so far.
- FACs 1 and 2 FAIL status was recorded only between 4 and 8 seconds after the stall warning was recorded.
This is very strange if the FACs really failed late, because with all flight control computers working (no other shows FAIL on the FDR), the aircraft should be in normal law, and there should be no stall warning.
IF FAC failure is recorded with some delay, the following becomes plausible:
- Aircraft at high angle of attack (well into the ALPHA-PROT regime, but still short of ALPHA Floor)
- low airspeed
- No stall warning, as aircraft in fully protected mode ("normal law")
- both FACs fail (within a single FDR data sampling period)
- Aircraft now in direct law (gear down), with no protections
- Stall warning sounds, as flight parameters are already "close to stall", and protections are lost
At least two factors making recovery very hard or impossible:
- Pitch trim at full nose-up. Airbus FBW aircraft autotrim pitch loads in normal law, even without autopilot.
- Low altitude.
Given the previous comments about covering air data orifices and vanes prior to painting/maintenance, one can speculate that something went wrong there, other than that it seems very unlikely that both FACs would fail at the same time.
Bernd