Definition
A small auxiliary surface attached to the trailing edge of a primary flight control that performs two functions at once: it moves automatically opposite the control surface to reduce the pilot's control force (balance tab function), and it can also be adjusted by the pilot from the cockpit to hold a desired trim setting (trim tab function).
Plain English
It is a single small flap on the back edge of a control surface that does two jobs: it lightens the force needed to move the controls, and it can be set by the pilot to keep the aircraft flying steady without holding pressure on the yoke or rudder pedals.
Context Anchor
Seen in flight control system discussions, especially when studying tabs on elevators, rudders, and ailerons.
Derivation
"Combination" because one tab combines two roles. "Trim" comes from the nautical sense of adjusting a vessel to ride level. "Balance" refers to offsetting (balancing out) the aerodynamic load the pilot would otherwise have to hold. "Tab" simply means a small attached piece — here, a small movable surface on the back of a larger one.
Why Pilots Care
Reduces pilot workload by combining force reduction with trim capability in a single device.
Intuition Check
“Balance” here does not mean balancing the airplane’s weight. It means using air pressure on the tab to reduce the force needed to move or hold a flight control.
Example Sentence 1
The elevator on this aircraft uses a combination trim and balance tab, so adjusting nose-up trim also lightens the pull force during the climb.
Example Sentence 2
During preflight the pilot checked that the combination trim and balance tab moved freely with the elevator.