A320 STALL & STALL RECOVERY

WHAT IS THE STALL:

 stall is a condition in aerodynamics where the Angle of Attack (AOA) increases beyond a point such that the lift begins to decrease. As per basic aerodynamic rules, the lift coefficient (CL) increases linearly with the AOA up to a point where the airflow starts to separate from the upper surface of the wing. At and beyond this point, the flight crew may observe: • Buffeting, which depends on the slats/flaps configuration and increases at high altitude due to the high Mach number • Pitch up effect, mainly for swept wings and aft CG. This effect further increases the AOA.

If the AOA further increases up to a value called AOAstall, the lift coefficient will reach a maximum value called CL MAX. When the AOA is higher than AOAstall, the airflow separates from the wing surface and the lift coefficient decreases. This is the stall.

NOTE: The stall will always occur at the same AOA for a given configuration, Mach number and altitude.

Influence of slats and flaps on Lift Coefficient versus Angle of Attack :

Slats and Flaps have a different impact on the Lift coefficient obtained for a given AOA. Both Slats and Flaps create an increase in the maximum lift coefficient.

Influence of speed brakes and icing on Lift Coefficient versus Angle of Attack :

speed brake extension and ice accretion reduce the maximum lift coefficient. Flight control laws and stall warning threshold take into account these possible degradations. To summarize, loss of lift is only dependant on AOA.

The AOAstall depends on: ‐ Aircraft configuration (slats, flaps, speed brakes) ‐ Mach and altitude ‐ Wing contamination .

HOW TO IDIENT THE STALL : 

The aural stall warning  : is designed to sound when AOA exceeds a given threshold, which depends on the aircraft configuration. This warning provides sufficient margin to alert the flight crew in advance of the actual stall even with contaminated wings.

Stall Buffet : Buffet is recognized by airframe vibrations that are caused by the non-stationary airflow separation from the wing surface when approaching AOAstall. When the Mach number increases, both the AOAstall and CL MAX will decrease. The AOA stall warning is set close to AOA at which the buffet starts. For some Mach numbers the buffet may appear just before the aural stall warning.

FOR STALL RECOVERY PLEASE REFER TO THE  (QRH ) AND FCOM .