Definition of the Stall: An aerofoil is said to have stalled when it reaches an angle of attack at which the airflow separates over the upper surface, dramatically reducing lift and usually inducing a nose down pitching moment. This occurs after the aerofoil has reached its critical angle - the angle at which the amount of lift that can be created by the aerofoil has reached a maximum. The effect of separation is to increase the pressure on top of the aerofoil, and so reduce the pressure differential the wing still receives some lift from the dynamic pressure under the wing, but it is insufficient to support the weight of the aircraft.

When the term stalling speed is applied to an airplane, this is taken to mean the IAS at which an aircraft stalls when it landing gear and flaps are retracted ( not applicable to Thruster), the throttle closed, and IAS reduced in straight and level flight and the aircraft is at Maximum All Up Weight (MAUW). However, since the stall is merely a function of angle of attack, the aircraft can be stalled at any speed and in any attitude. When propeller driven aircraft are under power, the propeller slipstream washing over the wing will delay the onset of the stall, below the 'clean' stalling speed