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 or circuit. It’s essentially a safer minimum speed for manoeuvring, typically higher than the calculated Vs₁ (stall speed in the clean configuration) or Vx/Vy (best angle or rate of climb), and is designed to provide a buffer above stall speed.

DMMS is calculated by multiplying Vs₁ by 1.404. This provides a margin to account for bank angles, turbulence, and minor handling deviations, helping ensure the aircraft remains safely above the stall during low-speed manoeuvres. The concept is derived from the Advanced Qualification Program (AQP) used in commercial training, and adapted for GA by safety advocates.

The use of DMMS is often recommended in GA, particularly in the traffic pattern or during low-altitude manoeuvring, to help avoid common risks like stalls during the base-to-final turn. Pilots are encouraged to maintain at or above DMMS until final approach, at which point V_ref (typically 1.3 × Vs₀) becomes the target.

Note: While angle of attack (AoA) — not airspeed — is the true cause of a stall, airspeed remains a practical and essential proxy in most GA aircraft without AoA indicators. DMMS helps protect against unintentionally exceeding the critical AoA during manoeuvring flight by keeping airspeed safely above stall margin.

Using DMMS improves safety during critical flight phases by maintaining a safe margin over stall, helping to reduce loss-of-control accidents.