What is the relation between INS position and GPS position when flying?

• A. They must always be identical
• B. They may diverge and require updating if the divergence exceeds a mile
• C. They are never compared
• D. They are only used during emergencies

Answer: (B)

INS position and GPS position come from different methods. The INS calculates position by continually integrating the aircraft’s measured acceleration and rotation, which means even tiny sensor biases accumulate into growing position errors over time. GPS gives an independent, highly accurate position fix from satellites. Because INS drift is unavoidable, the two estimates can diverge. In flight, navigation systems blend the two, and when the difference between the INS-derived position and the GPS position becomes large—often described in training materials as about a mile—the system updates or realigns the INS solution using the GPS data. So they aren’t always identical; divergence can occur, and a GPS-aided update corrects the INS drift to keep the overall navigation solution accurate.