What is the minimum height for the use of autothrottle during takeoff, either automatic or manual?

The minimum height for the use of autothrottle during takeoff, whether in automatic or manual mode, is indeed 400 feet. This altitude is established to ensure that the aircraft has achieved adequate performance and stability after takeoff before engaging the autothrottle system.

At lower altitudes, particularly those below 400 feet, pilots must maintain direct control of thrust to effectively manage the aircraft's climb performance during critical phases of flight. Engaging autothrottle too early can lead to a less responsive handling of thrust adjustments in the event of an unexpected situation, such as an engine failure or requiring a go-around.

After reaching 400 feet, the aircraft is typically in a safe climb profile where the necessary parameters for autothrottle engagement are met, allowing for smoother management of power settings as the aircraft continues to climb. This operational guideline helps enhance safety and operational efficiency during the crucial takeoff phase.