PuraVidaTransport:
When the plane reverted to Alternate Law (2B if I remember correctly),
engaging the autopilot was not an option. Once latched into alternate law, the autopilot can not be reengaged until the system is reset on the ground.
alogobotur:
Thx for the AP answers. So, AP switching on was not an option at all. It was also technicaly impossible.
In fact its a little bit more complicated.
The AP(AUTOMATIC FLIGHT) can be engaged in both NORMAL as ALTERNATE LAW!.
The AP has its own 'law' built in and 'bypasses' the
MANUAL control laws inside the FCPC(aka PRIM).
The AP commands direct flight surface deflection orders to the FCPC, the role of FCPC in automatic flight is to limit those orders when it 'senses' to be required so and to transfer the surface commands to the slaved FCPCs and FCSCs and their respective servos.
The AP however needs reliable airspeed parameter (to set the gains) and VLS(lowest selectable speed) to be available for operation and that was absent in this case.
PuraVidaTransport:
I find that response time to pilot inputs awfully slow
Apart from the explained SS algebraic addition:
Due to missing airspeed parameters, the filtergains of the flight control law were set to a fixed high speed value (IIRC 330KT).
This combined with the rather small integral(in time) part of the SS order resulted in this 'sluggish' elevator reaction but as one can extract from the FDR traces the reaction of the aircaft was a negative pitch and a positive Nz as commanded.