A ground proximity warning system monitors the flight path angle or barometric or inertially derived descent rate of the aircraft and modulates the glide slope alerting function in accordance with flight path angle or descent rate when the aircraft is not descending rapidly even though it is below the glide slope in order to reduce nuisance warnings without compromising system sensitivity. Alternatively, the repetition rate of the alert may be varied as a function of the flight path angle or descent rate to provide less frequent alerts when the aircraft is not descending rapidly.
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