What is the minimum airspeed to deploy flight spoilers?

The minimum airspeed required to deploy flight spoilers is generally determined by the aircraft's design and operational limits. In this case, the correct answer is Vref+10. This airspeed is above Vref, the reference stall speed in a landing configuration, ensuring that the aircraft maintains adequate control and aerodynamic stability during the deployment of the spoilers.

By deploying the spoilers at this increased airspeed, pilots can ensure that the aircraft is in a safe range to effectively manage lift and drag, as well as maintain controlled descent and landing performance. Spoilers are used for reducing lift and increasing drag, and deploying them at too low an airspeed could lead to control issues or an unstable situation during landing.

While Vref indicates the stall speed in the landing configuration for the aircraft, adding speed (like the 10 knots in this case) provides an additional safety margin. This helps to ensure that there is enough authority to manage the aircraft's pitch and roll moments when spoilers are activated, which is essential for safe flying during approach and landing maneuvers.