Definition
To lock the gimbals of a gyroscopic instrument, holding the gyro in a fixed position so it cannot move freely on its axes. Caging is used to protect the gyro during rough handling, taxiing, or aerobatic flight, and to reset certain gyroscopic instruments to a known reference.
Plain English
To temporarily lock a spinning gyro instrument in place so it stays still instead of swinging around freely. Pilots cage a gyro to protect it or to reset it to a known starting point.
Context Anchor
Seen in maintenance and operation of older attitude indicators and other gyro-based flight instruments.
Derivation
From the everyday word 'cage,' meaning to confine or hold something in place. In an instrument, the gyro is normally free to move on its gimbals; caging it 'pens it in' so it cannot move.
Why Pilots Care
Caging at the wrong moment can disable the instrument when it is needed, and failing to uncage after a reset leaves the instrument frozen and useless. Knowing when an instrument has a caging knob — and when it does not — is part of preflight and inflight awareness.
Analogy
It is like locking a delicate compass needle in place before moving it, so the moving part is protected instead of being allowed to swing freely.
Intuition Check
Cage does not mean putting the whole instrument in a physical box. Here it means locking the instrument’s internal moving gyro parts in a fixed position.
Example Sentence 1
Before starting aerobatic maneuvers, the pilot caged the attitude indicator to protect the gyro from tumbling.
Example Sentence 2
During aerobatic practice the pilot caged the heading indicator to protect the gyro from damage.