The FMS determines aircraft position by combining ___________________________.

• A. GPS position data
• B. All of the above
• C. Inertial reference system (IRS) heading data
• D. Air data computer (ADC) true airspeed and altitude reference

Answer: (B)

Position determination in an FMS comes from fusing multiple navigation inputs to produce a reliable location estimate. GPS provides the aircraft’s absolute position with high accuracy, giving a current fix on the map. The inertial reference system supplies heading and velocity data from onboard gyros and accelerometers, which supports dead-reckoning and continuity of navigation when GPS signals are unavailable or degraded. The air data computer delivers true airspeed and altitude, which feed the calculations that convert air-relative motion into ground-track information and leg distances, helping to update the position along the route. By combining all of these sources, the FMS maintains a robust and accurate position solution, even when one sensor is challenged.