At what airspeed must reverse thrust be reduced to idle after landing?

The correct airspeed at which reverse thrust must be reduced to idle after landing is 60 KIAS. This airspeed is predetermined to ensure safety and control of the aircraft during the landing rollout phase.

Reverse thrust is typically used to help the aircraft decelerate after touchdown, but it can affect the directional control, especially at lower speeds. Reducing reverse thrust to idle at 60 KIAS allows the pilot to maintain better control of the aircraft while transitioning from a high deceleration state into a stable and controllable speed for landing roll through to taxiing.

Maintaining reverse thrust beyond this airspeed could lead to challenges in controlling the aircraft and could affect the landing distance. The 60 KIAS threshold is established as a guideline based on aircraft handling characteristics and landing dynamics, ensuring that the pilot has adequate control authority when the reverse thrust is no longer in use.