Definition
Flight control systems in which the pilot's input is amplified or boosted by a mechanical, hydraulic, or electrical device, so that a small force on the controls produces a larger movement of the control surface. In the context of the Vertical Speed Indicator, the term refers to the internal mechanism inside the instrument that uses a calibrated leak and diaphragm to mechanically drive the needle, rather than to cockpit flight controls.
Plain English
A system where a small input is boosted by a helper mechanism to produce a larger output. Inside the VSI, this means a tiny pressure difference is used to move the needle through an internal mechanical assist.
Context Anchor
Seen in instrument and automatic-control discussions, especially where aircraft systems use sensed information, such as rate of climb or descent, to help control aircraft movement.
Derivation
From Latin servus, meaning 'servant.' A servo is a helper device that does work on behalf of the operator. Knowing this makes the idea easy: the system 'serves' the pilot by amplifying a small input into a larger result.
Why Pilots Care
Understanding that the VSI uses an internal servo mechanism helps explain why it has a slight built-in lag — the needle responds to pressure change through a mechanical assembly, not instantly. More generally, knowing what 'servo-assisted' means helps a pilot read system descriptions across many aircraft systems without confusion.
Analogy
It is like power steering in a car. You still steer, but a powered system helps move the wheels so less effort is needed.
Intuition Check
Servo-assisted does not mean the controls are fully automatic. It means a powered device helps move the controls after a command is given.
Example Sentence 1
The VSI uses a servo-assisted mechanism inside the instrument to translate small pressure changes into clear needle movement.
Example Sentence 2
During preflight the instructor demonstrated that servo-assisted controls still allow full manual override if the servo system fails.