A flight envelope protection system generates a control signal when the aircraft exceeds some flight envelope limits. The main functions of the Flight Envelope Protection (FEP) system are:

• the stall protection (with the stick shaker),
• the bank angle protection,
• the pitch angle protection,
• the speed protection (overspeed or low energy state).

The overspeed protection will inhibit the nose down pitch trim orders to prevent the aircraft from pitching further down in case it is over speeding because of a trim runaway. Some aircraft such as the Airbus, will even automatically pitch up to lose some speed, once the aircraft reaches a certain Mach Number.