What is DMMS and how is it calculated?

DMMS (Defined Minimum Manoeuvring Speed) is a practical safety speed used in General Aviation (GA) to prevent loss of control during the most critical phases of flight—low altitudes and manoeuvring, such as in the traffic pattern/circuit. It’s essentially a modified and safer minimum manoeuvring speed, often higher than the calculated Vs₀ (stall speed in landing configuration with full flaps) or Vx/Vy (best angle or rate of climb speeds), designed to give a buffer above stall speed.

DMMS is calculated by multiplying Vs₀ by 1.404, providing an additional margin to account for manoeuvring, gusts, and bank angle changes, ensuring the aircraft stays safely above stall speed during low-speed operations. This concept is based on the Advanced Qualification Program (AQP) often used in airline training, and has been adapted for GA by some pilot safety advocates.

Some recommend the use of DMMS in GA, in particular within the traffic circuit or pattern to avoid common risks, such as base-to-final turn stalls, especially during low-altitude manoeuvring. By flying at or above DMMS, pilots add a layer of safety during critical phases of flight, enhancing their ability to recover from sudden aerodynamic changes or mishandling. The recommendation is to use DMMS until final, when V_ref should be used.

Use of DMMS ensures safer manoeuvring during critical phases of flight, providing a buffer over stall speeds to improving pilot safety and reduce common accidents.