Which of these is a feature of secondary flight controls?

Secondary flight controls are designed to enhance the handling characteristics of an aircraft and assist the pilots with control movements. Unlike primary flight controls, which include ailerons, elevators, and rudders that directly control the aircraft's pitch, roll, and yaw, secondary flight controls such as flaps, slats, and spoilers serve to modify the aircraft's aerodynamic properties, making it easier for pilots to manage the aircraft in various flight conditions.

By providing additional lift, reducing stall speeds, or increasing drag, these secondary controls enable more precise handling and can also aid in landing and takeoff performance. Their primary purpose is to support and enhance the pilot’s ability to control the aircraft rather than serve as standard control inputs.

The other options refer to functions that are not aligned with the purpose of secondary flight controls. For example, manipulating engine power is more related to thrust management, and speed is typically controlled through throttle inputs and not solely dependent on secondary controls. Similarly, the main controls for directional changes are specifically the primary flight controls, which have a direct impact on the aircraft's navigation and orientation in the sky.