EASA learning objective 022.08.03.01.03 states 'Explain the following functions of the FEP: stall protection; overspeed protection'

Flight envelope protection (FEP) systems are designed to actively prevent the aircraft from leaving its allowable flight envelope. Limits protected by a FEP system include:

• Stall protection or prevention
• Overspeed protection or prevention
• Bank ange limits
• Pitch angle limits
• G load limits
• Low energy protection

On fly by wire aircraft this is relatively easy to implement as the flight control computers can ignore pilot inputs to keep the aircraft within the flight envelope. On aircraft with conventional controls stall and overspeed prevention is possible but pitch and bank angle protection aren't practicable.

Stall prevention on an aircraft with conventional controls involve physically preventing a stall by lowering the nose of the aircraft to reduce the angle of attack. A device called a 'stick pusher' physically moves the control column forward to prevent a stall occuring but this will always be preceeded by a stall warning.

A stall warning system (SWS) is required to give adequate warning of an approaching stall by using a unique and multi sensory warning. The pre-stall buffet is almost undetectable on large aircraft so a 'stick shaker' vibrates the control column to replicate this buffet as a warning to the pilots.

Technically the stick shaker is a flight warning system (FWS) device rather than an FEP device but as 'stick pusher' isn't given as an answer choice it's the most correct of all the options.

Dynamic trim --> INCORRECT. 'Dynamic' trim is not part of a FEP system

Rudder ratio limiter --> INCORRECT. Limits rudder movement as IAS increases, not part of a FEP system.

Mach tuck under --> INCORRECT. Describes the nose down aerodynamic tendency of an aircraft as it approaches M_crit

Stick shaker --> CORRECT. This is a warning rather than a prevention device but it's the most correct option in the absence of 'stick pusher'