Stall margin is the difference in the critical angle of attack and the angle of attack in which you are operating.

Example:

Suppose, critical angle of attack= 15°

AOA operating in a flight= 5°

then, Lift by the wing balances the weight of the airplane with a STALL MARGIN= 10°

Stall Margin is being controlled by an angle of attack and the position of flap control..

CHEERS!

Airbus aircraft do not use stall vanes for stall warning. Airbus use a sophisticated system of stall prevention instead, with the angle of attack and slat settings are primary parameters in the fly-by-wire computer system.

The angle of attack is determined by two electrically heated alpha probes on either side of the forward fuselage.

As the aircraft approaches a stall condition, (in normal law) the flight computers take control and return controls to a non-stall position.