Plain English Meaning

A navigation system that tracks where the aircraft is by sensing every movement it makes from a known starting point. It works entirely on its own, with no help from outside signals.

Full Definition

A self-contained navigation system that determines an aircraft's position, velocity, and attitude by continuously measuring its own accelerations and rotations using internal sensors (accelerometers and gyroscopes), starting from a known initial position. It requires no external signals such as radio aids, GPS, or ground stations to operate.

Context Anchor

Seen in autopilot and navigation discussions, where the aircraft’s guidance equipment needs reliable information about position and movement.

Derivation

From Latin ',' meaning 'inactivity' or ' to change in motion.' The system measures the aircraft's resistance to changes in motion (its accelerations and rotations) to figure where it has moved. The name reflects that the system relies entirely on the of motion itself, not on .