Inertial Navigation System

An Inertial Navigation System (INS) — or its modern evolution, the Inertial Reference System (IRS) — is a self-contained navigation system that uses accelerometers and gyroscopes to continuously calculate the aircraft's position, velocity, and attitude without relying on any external references (radio signals, GPS, or ground stations).

The system works by measuring accelerations in three axes and integrating them over time to determine velocity and position changes from a known starting point. Before departure, the system must be initialized with the aircraft's precise position (entered manually or via GPS) and undergoes an alignment process lasting 5-15 minutes during which the gyroscopes stabilize.

INS/IRS provides:

• Position (latitude/longitude)
• Ground speed and track
• True heading (independent of magnetic variation)
• Attitude (pitch, roll, yaw) for the flight instruments
• Wind calculation (when combined with air data)

INS drift (gradual accumulation of position error) is typically 1-2 nautical miles per hour. Modern aircraft use hybrid navigation, where IRS is continuously updated by GPS and DME to maintain accuracy of a few meters.