Which system is normally engaged after takeoff to set power in flight?

The Autothrust (A/THR) system is designed to automatically control the thrust produced by the engines of the A320 aircraft after takeoff. Once the aircraft is airborne and reaches a certain altitude, this system typically engages to maintain the desired speed set by the flight crew, optimizing engine performance and enhancing fuel efficiency during flight.

The A/THR system is particularly useful because it automatically adjusts throttle settings in response to changes in flight conditions, external winds, and pilot instructions. This allows the pilots to concentrate on other flight management tasks without having to manually manage engine power, contributing to overall safety and operational efficiency.

In contrast, while throttle control manages engine power, it does so manually unless the A/THR is engaged. The Speedbrake System is used primarily to slow the aircraft during descent and landing rather than to control thrust in flight. The Flight Management System (FMS) primarily assists with navigation and flight planning but does not directly manage engine power in the same way as the A/THR. Hence, A/THR is the correct choice for systems that engage after takeoff to set power in flight.