When discussing the different laws and its effect to the flight control system it is imho important to know and accept, that there are different Alt Laws available . In the last few post those differences didn´t get any attention (see my last post).
ALt Law 2B differs substantially from the other alt Laws, as all protections except load factor protection is lost. The biggest difference being, that in this Alt2b law the FCS works along the Nz law with no high speed stability (VMO2) or low speed stability protection (Vc prot) present.
Here the details of those protections in ALt Law (not in Alt2B):
Vc PROT law
This law, elaborated in the FCPCs, can be engaged in the flight and flare
phases, in the event of loss of the ALPHA1 law. It replaces the Nz law when
the aircraft speed becomes less than a threshold (Vc PROT).
A pitch order on the side stick then directly commands an elevator deflection
order to which a stability order with limited authority is added. The gains
of the Vc PROT law depend on the slat and flap position.
The purpose is to regain a positive static stability when approaching stall.
High Speed protection
This law, elaborated in the FCPCs, can be engaged in the flight and flare
laws. It permits, while staying in the Nz law, to add to the pilot’s orders a positive load factor when the aircraft speed or Mach number exceeds a certain threshold. In normal conditions (VMO1 law), the pilot’s authority is reduced in the nose down direction in order to make this protection not overrideable.
In degraded conditions (VMO2 law), the pilot’s authority is not reduced.
The purpose of the high speed protection is to limit speed or Mach excursions
beyond VMO or MMO, by adding a positive static stability.
Both those limited protections had not been available.
ALTERNATE LAW WITHOUT PROTECTION
In this case, the pitch protections are lost except the load factor protection.
This alternate law without protection is activated in the FCPCs after a triple
ADR failure.
When discussing the the stability and control issues as well as the stall entry of AF447 that point makes quite a difference. It´s the cause, that a SS in neutral on the way up to the apogee would have changed nothing, as the Nz-Law would have been active all the way into the stall. It may also be the reason, that in Dozys experiment in the A320 simulator a permanent stick force was required to maintain the pitch into the stall, or that the THS trim stopped, as VCprot worked against it or that PJ2 couldn´t achieve the same pitch as AF447 did in his simulation.
It might also make the difference between some of the other UAS flightpath excursions gone well.
If i would have to grade the handling in the different laws from a theoretical standpoint, it would be kinda
- Normal Law (artificial neutral stability with full protections)
- Alternate LAw except ALT 2b (artificial neutral stability with limited protections)
- Abnormal law (artificial neutral stability with limited protections without autotrim)
- Direct Law (natural positive stability)
- Alternate Law 2b (artificial neutral stability without protections except g-load protection)
But again, i didn´t fly that aircraft, but i doubt that all pilots are familiar with the consequences of all the different laws, as graceful as they may be (gums i´m with you on that one).
Edit:
It would be interesing to know, if the law Alt2b changed intermittently when the speeds came back on line or the above limited protections reactivated itermittently.