Localizer Capture Using GPS-Based Rectilinear Conversion
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Solution Overview
Problem
Current aircraft systems face challenges in accurately converting angular ILS deviations to rectilinear deviations, leading to inconsistent localizer captures and increased overshoots due to inaccurate distance estimates, especially when terrain effects, varying runway lengths, and unusual glideslope angles are encountered.
Innovation Solution
A method that computes the distance from the aircraft to the localizer transmitter using geographic positions and runway azimuth, allowing for accurate conversion of angular localizer deviations to rectilinear deviations, independent of assumptions about terrain and glideslope angles, thereby improving localizer capture performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the distance estimate is formed using radio altitude and glideslope error, then the conversion from angular ILS deviation to rectilinear ILS deviation can be performed, but the distance estimate becomes inaccurate due to terrain effects, varying runway lengths, and unusual glideslope angles
Solution Approach 1:
The patent replaces the traditional method of estimating distance using radio altitude and glideslope error (which relies on terrain and approach geometry assumptions) with a GPS-based geometric calculation method. The system computes distance directly from geographic coordinates of the aircraft, runway threshold, and localizer transmitter, eliminating dependence on terrain effects and varying glideslope angles.
Solution Approach 2:
The patent introduces GPS geographic position data as an intermediary to bridge the gap between angular ILS deviation measurements and rectilinear distance calculations. By using GPS coordinates as the intermediate reference frame, the system can accurately compute distance to the localizer transmitter without being affected by terrain variations or unusual approach geometries.
2Reliability
If control law gain is reduced to compensate for conversion errors, then robustness to a wide array of destination facility properties is achieved, but localizer capture performance is degraded
Solution Approach 1:
The patent replaces the error-prone conversion process (angular to rectilinear deviation using estimated distance) with a direct GPS-based geometric calculation approach. This substitution eliminates the need for gain reduction compensations, allowing the control law to maintain both robustness and high performance across diverse facility properties.
3Measurement precision
If the aircraft begins localizer capture maneuver only after reaching the course guidance sector, then the aircraft is within the reliable indication zone, but the physical distance available to complete the turn is insufficient, causing overshoot
Solution Approach 1:
The patent enables the aircraft to initiate the localizer capture maneuver in advance, before entering the narrow course guidance sector, by providing accurate distance and bearing information through GPS-based calculations. This preliminary action allows sufficient distance to complete the turn while maintaining capture accuracy through the converter's precise rectilinear deviation calculations.
Data Source
AI summary
Instrument Landing System ("ILS") localizer captures have historically been prone to performance degradations based upon erroneous estimates of the localizer deviation and deviation rate. The angular nature of the ILS beam and the relatively narrow trusted linear course guidance sector of the beam are the primary causes of many such issues. It is highly desirable to convert the angular guidance data into a rectilinear form when used by an autopilot and/or flight director systems, the latter of which allows for more consistent stability and performance with respect to distance to runway threshold. Systems and methods disclosed herein are for accurately converting angular localizer data into rectilinear localizer data, thus allowing for improved localizer capture performance and stability.