@DW, HN, and MB,
we had been through this discussions many moons ago.
In Alt2 we have the NZ Law without protections.
Source LH TTM
Nz law
This law, elaborated in the FCPCs, is the normal pitch law engaged in the
flight phase.
Through a pitch action on the side stick, the pilot commands a load factor ;
the Nz law achieves this command, depending on the aircraft feedbacks, so
that:
- The short-term orders are achieved by the elevator servo controls.
- The long-term orders are achieved by the THS actuator (autotrim function).
The gains depend on the Vc, on the flap and slat position and on the CG
location.
The pull on the stick sends a loadfactor demand to the FCPC, which in turn position the elevators and in the long term the THS. There is no direct conection SS to elevator.
When the PF pulled back on the stick for some time, he commanded a loadfactor increase, which the aircraft could not achieve neither by elevators nor by THS trim after 02:11:30. Therefore position of elevators are full NU and the THS was NU as well. Relaxing the SS to neutral would reduce the loadfactor to 1 G, which the aircraft could not achieve either in the stalled state, therefore no change in elevator position or THS trim, the FCPC´s still try to achieve the demanded loadfactor of 1 G (stick neutral) which would be a solid climb with the 10° pitch at release of the SS.
Only prolonged SS ND command would have started to move the elevators from Full NU to ND position.
Especially DW´s inputs are wrong and misleading concerning the behaviour of NZ law and giving the impression, that the elevator position can be correlated with the SS position, like releasing SS to neutral would have neutralized the elevators. That would be the case in an unstalled flight condition, where you point the nose with SS, then neutralize and the aircraft continous with one g flight on the new ordered trajectory.
But in the stalled condition AF 447 was in, the actual flight trajectory was 45° down and the ordered one was some 10° climb, which neither elevators nor THS could give, but the FCPC´s tried to achieve by elevator and THS full NU.
Obviously the crew did not understand the situation and the law and the consequences of that situation like some posters here. SS input from full NU to some short ND didn´t produce any noticeable response of the aircraft. Those pitch responses present had been mainly caused by thrust changes and not by SS inputs. Way back there was a graph with SS pitch input, elevator position and thrust setting, that one told it all.
The elevator never came in the ND region after the initial stall, the best it ever got was 15° NU command at 02:12:45 and 02:13:50 (page 108 of BEA interim report No. 3) when just prior the thrust was reduced and the SS was more ND then NU.
franzl