Definition
To lock the gimbals of a gyroscopic instrument so the spinning rotor is held in a fixed position relative to its case, preventing it from precessing or tumbling during ground handling, aerobatics, or unusual attitudes. Caging is done by pulling or rotating a knob on the instrument face that mechanically restrains the gimbal assembly.
Plain English
To lock a spinning instrument in place so it cannot swing around and get knocked off its reading. The pilot or technician pushes or pulls a knob on the instrument to hold the moving parts still.
Context Anchor
Seen in maintenance instructions and in older cockpit instruments that have a cage or uncage control.
Derivation
From the everyday word 'cage,' meaning to confine or restrain something inside an enclosure. The gyro's moving gimbals are 'caged' — held still inside the instrument case — so they cannot swing freely.
Why Pilots Care
An uncaged gyro can tumble during steep maneuvers or rough handling, giving false readings or damaging the instrument. Knowing when to cage and uncage a gyro protects both the instrument and the accuracy of the indication the pilot relies on.
Intuition Check
Do not read cage as the everyday idea of putting something inside a cage. In aircraft instruments, cage means lock or restrain a moving mechanism.
Example Sentence 1
Before starting aerobatic maneuvers, the pilot caged the attitude indicator to keep the gyro from tumbling.
Example Sentence 2
Before rough handling on the ramp, the mechanic caged the directional gyro to protect its rotor.