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On all jet engines, but particularly on high bypass ratio engines, the engine acceleration profile is not linear. It follows the engine control law that is defined to optimize the acceleration in a way that the risk of engine stall is reduced. It also takes into account the influence of the position of the engine installed on the aircraft and the effect on the airflow at the engine’s inlet due to its proximity to the ground and the surrounding aircraft structure.

Every engine has its own performance level due to manufacturing tolerances. In addition, engine performance evolves with time due to wear and ageing. As a consequence, the acceleration profiles may slightly differ from one engine to another on an aircraft, even if fitted with new engines. Similarly, the idle thrust can slightly differ from one engine to the other.

Taking into consideration both of these parameters, if the Fligh…

VS: Stalling Speed

For a conventional aircraft (not Airbus), the reference stall speed is based on a load factor that is less than 1g. This gives a Stall Speed that is lower than the stall speed at 1g (1 Gravity). See Figure B6. All operating speeds are expressed as functions of this speed (for example, VREF = 1.3 VS).

VREF: Reference speed, It's the steady landing approach speed required at a height of 50 feet above runway threshold for a defined landing configuration. It's used as a reference for calculating the final approach speed and the landing distance.

Coefficient of Lift Vs Angle of Attack

Because the A320 family aircrafts has a low speed protection feature that the flight crew can't override, (This is true meanwhile the aircraft remains in Normal Law) Airworthiness Authorities have reconsidered the definition of stall speed for the A320.