An Inertial Navigation System (INS) provides the aeroplane’s velocity and position by continuously measuring and integrating its acceleration. This system relies on no external references, is unaffected by weather, and can operate during the day or night.

The products of an INS are position (latitude/longitude), speed (kt), distance (nautical miles), and other navigational information.

An Inertial Navigation System is based on the measurement of acceleration in a known direction, or along a sensitive (input axis), which is detected and measured by an accelerometer.

For navigation in a horizontal plane, two accelerometers are needed, which are normally aligned with True North and True East.

To keep this reference valid, the accelerometers are mounted on a gyro-stabilised platform, which maintains the correct orientation during all aeroplane manoeuvres.