The Glide Path Simulator modes

1. Control Panel  Download (PDF - 1158kB)
The main module where all input parameters are loaded from the default setup file, which can be changed by each user according to the most used values. New values or simulated system errors can be entered with the arrow keys or a mouse directly on the screen. This works like a Spreadsheet where all feeds and physical distances (toggle between meters and feet) are instantly computed and displayed on the lower part of the panel when changing the basic input data in the upper part.


2. Lateral trace.
Simulation of an orbit crossover in the azimuth plane to see the deviation, SBO&CSB amplitudes or RF-phase at a given distance and elevation angle. This is a quick and efficient way of checking if the system feeds have drifted.

3. Vertical trace.
Simulation of the resulting Glide path deviation and amplitudes along a vertical line above given coordinates in the terrain. This mode is designed to check angle and sectors as well as clearance below and above the full sectors. The display can be a table, 2-Dimensional or 3-Dimensional graphic diagram. The graphics show the Deviation, SBO& CSB amplitudes and SBO&CSB phase. After a 2D vertical trace, the theoretical Glide path angle and sectors are computed.

The 3D graphs are identical to the 2D graphs while showing 13 curves side by side in different azimuth angles from -l2 to +12, making a curtain-like grid diagram. This will give an instant view of the sideways coverage of CDI and carrier field strength in the required 8 azimuth coverage sector. CDI, SBO, CSB and Clearance amplitudes can be shown either separately or all together in 4 smaller diagrams.

4. Window Overview.
This will display the ISO-Deviation lines from 300A fly up to 225A fly down in the coverage sectors of the GP system. This set of lines can be taken as a footprint of the system condition where even the smallest change in phase or amplitude in the feeds as well as small mechanical misalignments can be detected. Any change in this window indicates that something is going wrong. The main usage is diagnosis of erratic symptoms based on Flight Inspection measurements or as a tutorial tool to learn the impact of certain changes in the feeds and the environments.

The computed elevation angles and half sector widths at 8 and 0 azimuth are displayed with the window diagram. After a completed computation the values are stored in memory. A menu enables a quick look at the SBO, CSB amplitudes or the RF phases. The Window relates directly to the curtain (3D) diagram, and one can easily switch between these display modes while a computed window resides in the memory.

5. Approach mode.
Simulation of an approach path at either constant level, ideal hyperbolic line of constant zero deviation or tracked by a theodolite located at user-determined coordinates. After a Level Run the Glide path angle and sectors are computed, while after the Hyperbolic or Theodolite approaches, the average actual & achieved GP angles and Datum heights are found using a linear regression, the Least Mean Squares method. If reflection objects are entered into the terrain model, reflections may show bends and scalloping along the approach. Distance scale is either in kilometres, feet or Nautical Miles.

6. Fixed Position mode.
Simulation of the resulting deviation and amplitudes in one or two positions while a selected feed parameter is varied between chosen limits. Also the impact of increasing snow depth is simulated. The main purpose of this mode is to compare the far field and near field (monitor or test mast position) response to possible errors in the antenna system.

7. Ground Current.
Visualisation (2D or 3D) of the ground current induced on the reflection plane from the different glide path systems. As the total reflected signal from the ground plane corresponds to the total ground current, this mode is used to compare the available reflection plane area to the actual system requirements. When this reflection plane is limited, changes in system feeds will be seen to have significant impact on the signal quality along the approach path. M-ARRAY glide path can be optimised to operate satisfactory under such environment.


8. Bend Analysing.
This part will analyse the bend wave lengths and their position along the flight path to find the possible origin of the reflection object(s) as intersections of hyperbolic lines plotted on the ground. It can also reverse the process in computing the bend wavelength at selected distances by entering the coordinates of a suspected reflection object. This feature serves as tutorial tool for flight inspectors to gain experience in bend analysing. The approach mode will give a graphic presentation of the theoretical bend pattern of suspected reflection objects.

9. Utilities
Some useful utilities are included:

ADU Panel.
This is to simulate adjustments directly on a 'graphical' Antenna Distributing Unit (ADU), which can be brought up on the screen. The phase and amplitude ratios between the antennas can be adjusted by moving the controls with the arrow keys. One may also disconnect some signal components inside the Unit or one or two antennas (simulates terminating in 50 ohms).

MCU Panel
Three green numeric display fields on the Control Panel show the CDI/DDM from the Monitor Combining Unit (MCU) outputs.  These fields show monitor response to any setting of the Glide Path System parameters, such as antenna phase error settings, clearance transmitter power or deviation etc. The fields are preset to emulate THETA, 0.88 THETA and 0.45 THETA on the runway extended centreline, but can be set to any desired elevation angle for monitoring by means of changing the attenuation from the pickup loops in each antenna element. The proper attenuation and phasing of each pickup signal are automatically computed, but can be changed to any practical value in order to simulate errors or actual measured values in the MCU. The elevation angle of the DS channel (0.88 THTEA) can be adjustments directly on a 'graphical' MCU which can be brought up on the screen.

RPL Module.
The Reflection Plane (RPL) module will determine the average weighted slope of the reflection plane by entering measured terrain heights along a line in front of the antenna system. In addition to the slope, the correct zero height for the antennas will be found. The computation uses the least squares method as well as optical reflection geometry combined with estimated ground current for the actual GP antenna system. This method is based on many years of experience to find correct antenna heights during setup and will save a lot of flying time to verify antenna heights based on each elements lobing diagram, which might be very unreliable in adverse terrain. The resulting Forward Slope can be entered into the Control Panel by a key stroke.

 Nordic Air Navigation Consulting, Norway