At what airspeed must flight spoilers not be extended for safety margins?

The correct choice, indicating that flight spoilers must not be extended below Vref + 10, aligns with the operational safety protocols associated with the CRJ 900. Vref is the reference landing speed, which is critical in determining the minimum speed at which the aircraft can safely operate during approach and landing. Extending the flight spoilers while below Vref + 10 could compromise the aircraft’s controllability and increase the risk of an inadvertent stall, especially during the critical phases of landing where lower speeds are involved.

This operational limitation is put in place to ensure that pilots maintain adequate control of the aircraft, particularly given that extending spoilers at speeds too close to Vref could reduce lift significantly and lead to unwanted aerodynamic characteristics. By adhering to this speed restriction, pilots can maintain a safe margin above stall speed, ensuring that the aircraft remains in a stable flight condition during those critical phases.

In contrast, the other options present lower speeds that fall within a range where extending the spoilers could lead to issues with aircraft handling and safety. The choice of Vref + 10 as a minimum ensures that the aircraft retains sufficient lift and control authority, aligning with standard operating procedures for safe aircraft handling.