Bearfoil;
One thing, you mention a "disconnect" of AP does not degrade flight Law. I was of the impression an involuntary (auto) drop commanded Alternate Law? If Aero and accel considerations caused the A/P to quit, that does not trigger Law Change?? I have long believed the AP dropout was caused by its inability (programmed) to keep up?
An involuntary autopilot disconnect does not in itself result in any degrading to alternate 1 or 2, or direct law.
However, some system abnormalities or failure conditions which do result in a degradation to alternate or direct law also result in an involuntary disconnection of the autopilot and autothrust systems.
The difference is illustrated below - the following summarizes both crew-actioned autopilot disconnections and involuntary disconnections which would not be associated with any degradation of flight control laws:
AP DISENGAGEMENT
AP1 or 2 disengages when :
– The pilot presses the takeover pushbutton on the sidestick.
– The pilot presses the corresponding AP pushbutton on the FCU.
– The pilot pushes on the sidestick harder than a certain threshold. (Disengagement through rudder
pedals is only active on ground).
– The other AP is engaged, except when localizer/glideslope modes are armed or engaged, or rollout or go-around mode is engaged.
– Both thrust levers are set above the MCT detent and the aircraft is on ground.
– In a non-precision approach, with FINAL APP mode engaged, the aircraft reaches :
• The MDA/MDH minus 50 feet (if entered), or 400 feet AGL (if no MDA/MDH is entered), or
• The Missed Approach Point (MAP), depending on which one comes first.
– One of the engagement conditions is lost.
– Furthermore, in normal law with all protections available, the AP will disconnect if :
• High speed protection is active.
• Angle-of-attack protection is active (α prot + 1° is reached).
• Pitch attitude exceeds 25° up, or 13° down, or bank angle exceeds 45°.
The standard way for the flight crew to disengage the AP is to press the takeover pushbutton on the sidestick.
When AP is OFF, the associated FCU pushbutton goes off, and the “AP1” (or AP2) is removed from the PFD's FMA.
The following is a table of results/outcomes from various system degradations which result in alternate laws 1 or 2 or direct law, and an involuntary disconnection of the autopilot & autothrust systems:
Depending on the type of failures affecting the flight control system, or peripherals, there are 3 possible reconfiguration levels :
– Alternate law (ALT 1 or ALT 2)
– Direct law, or
– Mechanical.
