If the INS and GPS positions differ by more than one mile, what action should be taken?

• A. Update the INS to GPS position
• B. Ignore the difference
• C. Switch to GPS-only navigation
• D. Restart the INS

Answer: (A)

The main idea is that the inertial navigation system (INS) drifts over time because it relies on integrating accelerations, while GPS gives an independent position reference. When the INS position and the GPS position differ by more than a set tolerance (here, more than a mile), the best action is to update the INS to the GPS position. This realigns the INS solution with the GPS fix, correcting accumulated drift and restoring overall accuracy without losing the benefits of the inertial information.

Ignoring the discrepancy lets errors accumulate and degrades navigation accuracy. Switching to GPS-only discards the inertial data benefits and can be problematic if GPS is unavailable or intermittent. Restarting the INS would throw away useful drift estimates and throw the solution off again instead of applying the corrective GPS update.