A flight control module for computing localizer deviation during landing of an aircraft, the aircraft receiving instrument landing system, ILS, localizer signals and computing first and second multi-mode, MMR, localizer deviation signals based on the first and second ILS localizer signals, the flight control module comprising: a communication interface configured to receive inertial data for said aircraft, and configured to receive the first and second MMR localizer deviation signals from said aircraft; a processor coupled to said communication interface and configured to compute an inertial localizer deviation based on the inertial data; and a signal selection fault detection, SSFD, module configured to select one localizer deviation from among the respective first and second localizer deviations (424, 426) and the inertial localizer deviation for use in controlling an automated landing system of said aircraft; wherein said processor comprises a complementary filter configured to generate a filtered MMR localizer deviation based on the first and second MMR localizer deviation signals received through said communication interface and the inertial data, including a cross-runway acceleration, and wherein said processor is configured to: integrate inertial data, generated by an inertial reference unit, IRU, for the aircraft, from the filtered MMR localizer deviation to generate an inertial localizer deviation at the IRU; translate the inertial localizer deviation at the IRU to a guidance control point, GCP; initialize an inertial localizer deviation computation based on the filtered MMR localizer deviation, comprising latching the filtered MMR localizer deviation upon an altitude of the aircraft falling below a predetermined threshold. a communication interface configured to receive inertial data for said aircraft, and configured to receive the first and second MMR localizer deviation signals from said aircraft; a processor coupled to said communication interface and configured to compute an inertial localizer deviation based on the inertial data; and a signal selection fault detection, SSFD, module configured to select one localizer deviation from among the respective first and second localizer deviations (424, 426) and the inertial localizer deviation for use in controlling an automated landing system of said aircraft; wherein said processor comprises a complementary filter configured to generate a filtered MMR localizer deviation based on the first and second MMR localizer deviation signals received through said communication interface and the inertial data, including a cross-runway acceleration, and wherein said processor is configured to: integrate inertial data, generated by an inertial reference unit, IRU, for the aircraft, from the filtered MMR localizer deviation to generate an inertial localizer deviation at the IRU; translate the inertial localizer deviation at the IRU to a guidance control point, GCP; initialize an inertial localizer deviation computation based on the filtered MMR localizer deviation, comprising latching the filtered MMR localizer deviation upon an altitude of the aircraft falling below a predetermined threshold. integrate inertial data, generated by an inertial reference unit, IRU, for the aircraft, from the filtered MMR localizer deviation to generate an inertial localizer deviation at the IRU; translate the inertial localizer deviation at the IRU to a guidance control point, GCP; initialize an inertial localizer deviation computation based on the filtered MMR localizer deviation, comprising latching the filtered MMR localizer deviation upon an altitude of the aircraft falling below a predetermined threshold.