I was recently reading that in most military jets, auto-pilot can disengaged without hitting the button, by applying 5lbs of pressure to sticks.
Does this work in commercial airliners such as the A320?
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Yes. I’m not sure of the amount of force, but from the A320 FCOM:
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 or moves on the rudder pedals above a threshold.
- The pilot moves the pitch trim wheel beyond a certain threshold.
- The other AP is engaged, except when localizer/glideslope modes are armed or engaged, or when the rollout or go-around mode is engaged.
- Both thrust levers are set above the MCT detent and the aircraft is on the ground.
- The aircraft reaches the MDA-50 feet (MDH-50 feet), or 400 feet AGL if no MDA/MDH, with APPR mode engaged and a non-lLS approach is selected.
- 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°;
- A rudder pedal deflection is more than 10° out of trim.
The standard way for the flight crew to disengage the AP is to press the takeover pushbutton on the sidestick. When the AP is OFF, the associated FCU pushbutton goes off. and "APl" (or AP2) disappears from the PFD’s FMA.
While not an A320 per the OP's question, the case of Aeroflot Flight 593 in 1994 details a case where the partial disengagement of the autopilot on an A310 by means of continued pressure on the controls contributed to the crash. (massive oversimplification, look at the Wikipedia page linked above for more details)
The circumstances that led to the crash of Aeroflot 593 were addressed in later revisions of Airbus aircraft to the point where you would know it if the autopilot disengaged due to conflicting control stick inputs.
From what I could gather, airliners such as the Airbus A320 have a red button on the sidestick that will disengage the autopilot should you press it. The autopilot can also be disengaged by moving the control stick though this is not usually recommended as it can cause the aircraft to roll suddenly.
Airbus aircraft have an autopilot panel such as this one below that controls the autopilot:
Places I got my info from:
Hope this helps. And if anyone feels like I stole your info, I apologize.