How is the autothrust system armed on the ground?

The autothrust system is armed on the ground by setting the thrust levers to FLX with a FLEX temperature entered. When the thrust levers are positioned in the FLX range with an appropriate FLEX temperature, the autothrust system anticipates the use of managed thrust during takeoff. This allows the autothrust system to control the thrust delivered during the initial climb, taking into account the performance characteristics defined by the entered FLEX temperature.

The FLEX temperature is crucial as it allows the aircraft to take off with reduced thrust, which is beneficial for engine management and to maximize performance under certain conditions such as longer runways or favorable weight scenarios. By contrast, thrust lever positions that are either set to CLB or above IDLE do not arm the autothrust system in the manner required for takeoff performance optimization as these settings are reserved for different phases of flight where full climb power or thrust retardation is anticipated.