Tubby:
The abnormal attitude law is a subset of alternate law on the aircraft and is triggered when the angle of attack exceeds 30° or when certain other inertial parameters - pitch and roll - become greater than threshold levels.
........
Abnormal law could only have been triggered by an inertial upset, such as a 50° pitch-up or bank angle of more than 125°. "That never occurred," says French accident investigation agency Bureau d'Enquetes et d'Analyses.
From the BEA report:
"The angle of attack, when it was valid, always remained above 35 degrees."
More questions to answered by BEA!!!
From the AMM:
"Abnormal attitude law,
This FCPC law is engaged when certain aircraft parameters exceed pre-determined values.
This law ensures that the flight control law will never hinder aircraft recovery.
The laws available are:
- in roll: the yaw alternate law,
- in pitch: an adapted Nz law, without autotrim.
After aircraft recovery, and until landing, the laws available become:
- in roll: the yaw alternate law,
- in pitch: the Nz law (with recovered autotrim)"
"The Nz law is such that the aircraft response is quasi independent of aircraft speed, weight, and CG location.
If both ADIRUs are failed, the Nz law is kept, but with limited pitch rate and gains.
A consolidation of the vertical acceleration and pitch attitude rate is then performed via the two accelerometer units."
From the FCOM:
"An abnormal attitude law in pitch and roll is provided, if the aircraft is in flight and in any of these
conditions :
– Pitch attitude > 50° nose up or 30° nose down
– Bank angle > 125 °
– Angle of attack > 30° or < − 10°
– Speed > 440 knots or < 60 knots
– Mach > 0.96 or < 0.1
The law in pitch is the alternate law without protection (except load factor protection) and without auto trim.
In roll, it is a full authority direct law with yaw alternate.
After recovery, the flight controls laws are:
In pitch : Alternate law.
In roll : Direct law with yaw alternate law."
I think we already all concluded that it did enter -abnormal attitude law- but only after THS was auto-positioned in 13 ANU, and never recovered from this law.