What must aircraft flight control trim systems allow a pilot to do from the cockpit?

The trim systems in an aircraft are designed to help pilots maintain stability and control without continuous pressure on the control surfaces. Specifically, the primary function of flight control trim systems is to allow a pilot to adjust the position of the trim tab. By doing so, the pilot can achieve a desired orientation of the aircraft, reducing the need for constant manual input on the control yoke or stick. This aids in alleviating pilot workload and enhances flying comfort during long flights or when making minor adjustments during flight.

The ability to determine the relative position of the trim tab directly correlates to the effectiveness of the aircraft's control systems, allowing for fine-tuning of the aircraft's pitch, roll, and yaw. This precise control is essential for safe and efficient flight operations, especially during different phases of flight, such as cruise or landing.

In contrast, the other options do not pertain to the primary function of trim systems in the cockpit. Determining altitude corresponds to altimeter usage, adjusting engine power relates to throttle control, and controlling flaps and landing gear is concerned with different flight control systems altogether. These functions have their distinct mechanisms and controls separate from the trim systems.