A method comprises receiving an ILS transmission signal in an onboard ILS receiver during an aircraft approach, and receiving a GNSS position signal in an onboard GNSS augmentation system receiver during the approach. The method determines a first set of flight path deviations based on the ILS transmission signal, and a second set of flight path deviations based on the GNSS position signal. The first set of flight path deviations are sent to a first complementary filter, which outputs a first filtered deviations signal. The second set of flight path deviations is sent to a second complementary filter, which outputs a second filtered deviations signal. A scale factor is applied to the first filtered deviations signal or the second filtered deviations signal, such that the filtered deviations signals are normalized to the same scale. The method combines the normalized filtered deviations signals to produce a hybrid signal for further processing.