What is the primary function of an elevator trim tab?

The primary function of an elevator trim tab is to eliminate flight control pressures at varying airspeeds. When flying, pilots often experience varying control forces that can make it challenging to maintain level flight or a desired pitch attitude. The elevator trim tab provides a means to relieve these forces by adjusting the elevator's position without the pilot needing to exert continuous pressure on the control yoke or stick.

By moving the trim tab, usually located on the trailing edge of the elevator, it changes airflow characteristics around the elevator, which in turn helps to maintain the aircraft in a stable attitude. This feature is essential for reducing pilot workload, especially during long flights or in turbulent conditions, allowing the pilot to fly the aircraft with minimal continuous input on the controls.

In contrast, other functions referenced in the incorrect options do not align with the specific role of elevator trim tabs. Ailerons, engine thrust, and fuel flow adjustments are managed by different systems or controls within the aircraft.