Vertical required navigation performance containment with radio altitude

摘要

A monitor on-board an aircraft which uses radio altitude measurements as the basic observable altitude during runway approach. The basic concept utilizes the aircraft's navigation system, which includes means to store and retrieve radio altitude thresholds as a function of the distance along the desired path from the runway thresholds. These threshold functions are determined in advance based on a radio altitude reference which is defined as the expected radio altimeter measurement that would be made if the airplane were exactly on the desired reference path. Vertical containment monitoring is achieved by comparing the radio altitude measurement to computed thresholds for both too high and too low. During the approach, an annunciation message can be generated if the radio altitude measurement is above or below the threshold limits.

主权项

1. An onboard system for detecting deviation of true airplane vertical position from a desired reference path, comprising:
a database storing high and low radio altitude thresholds which vary as a function of horizontal distance from a runway threshold; a GNSS receiver for acquiring horizontal position measurements as the aircraft approaches the runway threshold; a radio altimeter for acquiring radio altitude measurements as the aircraft approaches the runway threshold; and a processor for computing a horizontal distance from the runway threshold using the horizontal position measurements and comparing each radio altitude measurement to a respective pair of said high and low radio altitude thresholds as the aircraft approaches the runway threshold.