Plain English Meaning

A navigation system that works on its own. Once you tell it where you are at the start, it keeps track of where you go by sensing every acceleration and turn. It needs no signals from outside the aircraft.

Full Definition

A self-contained navigation system that determines an aircraft's position, velocity, and attitude by continuously measuring its own acceleration in three dimensions, starting from a known initial position. It uses gyroscopes and accelerometers to track movement without relying on any external signals such as ground stations, satellites, or radio aids.

Context Anchor

Seen in aircraft navigation, instrument flight, long-range flight, and avionics discussions where the aircraft’s position must be tracked continuously.