If GPS data is degraded, what is the primary source of attitude, heading, and navigation information used by the aircraft?

If GPS data is degraded, what is the primary source of attitude, heading, and navigation information used by the aircraft?

• A. FMS data only
• B. Ground-based navigation beacons
• C. IRS/ADIRU data
• D. Magnetic compass

Answer: (C)

When GPS is degraded, the aircraft relies on the inertial reference system (IRS) / ADIRU for attitude, heading, and navigation data. The IRS uses onboard gyros and accelerometers to sense angular rates and linear accelerations, enabling continuous determination of the aircraft’s attitude (pitch and roll) and heading. It also provides a navigation solution by dead-reckoning from those motions, with updates from air data and occasional radio navigation inputs as available. This data is generated independently of GPS, so the flight control and FMS can maintain accurate attitude and heading information even when GNSS is unavailable. Magnetic compasses aren’t trusted as the primary source for navigation in flight because they are susceptible to local magnetic disturbances and can drift, especially at the scales involved in aviation. Ground-based navigation beacons require external infrastructure and do not provide the robust, continuous attitude data that the IRS supplies. The FMS uses IRS data as its primary navigation reference, and GPS serves as a corrective input when available.

When GPS is degraded, the aircraft relies on the inertial reference system (IRS) / ADIRU for attitude, heading, and navigation data. The IRS uses onboard gyros and accelerometers to sense angular rates and linear accelerations, enabling continuous determination of the aircraft’s attitude (pitch and roll) and heading. It also provides a navigation solution by dead-reckoning from those motions, with updates from air data and occasional radio navigation inputs as available. This data is generated independently of GPS, so the flight control and FMS can maintain accurate attitude and heading information even when GNSS is unavailable.

Magnetic compasses aren’t trusted as the primary source for navigation in flight because they are susceptible to local magnetic disturbances and can drift, especially at the scales involved in aviation. Ground-based navigation beacons require external infrastructure and do not provide the robust, continuous attitude data that the IRS supplies. The FMS uses IRS data as its primary navigation reference, and GPS serves as a corrective input when available.