Stall Warning System (SWS)
To prevent the aircraft from entering a stalled condition, a stall warning system (SWS) is installed in every aircraft. The stall warning will typically consist of an aural warning with a voice warning such as ‘STALL, STALL’, and a stick shaker connected to the control column.

Stall Protection system (SPS)
Some transport category aircraft are challenging to recover from stalled conditions. For these types, an additional Stall Protection System (SPS) is legally required that automatically prevents entry into a stall should the pilot not react appropriately to the stall warning.

Caution! The stall warning (stick shaker) is only alerting the pilot that the aircraft has entered a stall while the stick pusher is a protection – it acts on the control column to prevent the aircraft from entering the stall conditions.
The input data of the stall warning system are:

Angle of Attack

Configuration (slats/flaps deflection)

Note: A stick shaker is a stall warning device, therefore it is a (soft) flight envelope protection system.