Assessment of ILS protection areas impact on large aircraft operationsMethodology

ENAC

Selection of test points to be tested during real ground and flight measurements with an A380 aircraftSimulate these points with various modeling tools :To reduce the number of points to be measured to the most significant onesTo get some pre-measurement predictions in order to evaluate the prediction performances of the tools

Analyze the measurements and evaluate the impact of the A380 on the size of the critical and sensitive areas Compare the measurements with the predictions of the modeling tools and evaluate the correlation between simulations and measurements.

ILS simulation methodologySimulation of the radiation patterns delivered by the ILS Choose a method to simulate the propagation of electromagnetic waves and scattering on obstacles:

Method of MomentsMultilevel Fast Multipole MethodPhysical OpticsImproved Physical OpticsGeometrical Optics Geometrical theory of diffractionParabolic EquationEtc

Design a model of the object to evaluate (A380) that fits with the simulation method and represents the most critical parts involved in the scattering of electromagnetic waves Simulate the radiation pattern of the receivers antenna

Simulate the receiver signal processing Simulate the measurement path and receiver speed

ILS simulation toolsAXIS from NANCO, Oslo DOS program based on Physical Optics ATOLL from ENAC, Toulouse Windows program based on Physical Optics NPPM from OHIO University Windows program based on Physical Optics IHSS 3D modeling from NAVCOM Consult

ILS radiation patternsToulouse Blagnac 14R

Frankfurt 25L

A380 modelMost realistic modelUsed for calculations with the Method of Moments

A380 modelSimplified models used in the simulation tools based on Physical OpticsNPPM model

A380 modelPredominant impact of tailfinCSB Surface CurrentsSBO Surface CurrentsCalculated with EMC2000 from EADS using the Method of Moments

A380 modelSimplified models used in the simulation tools based on Physical OpticsATOLL and AXIS model

Radiation pattern of receiving measurements AntennasATOLL simulationsDFS antennaDSNA antenna

Receiver modelingReceiver impact on measurementsP11 bis at Toulouse airport (Forward= 2886, sideway = 178, rotation = -30)R&S EVS200 + DSNA antennaARTUS 324 + 45 turned dipole antenna

Receiver modelingReceiver and speed impact on measurementsP11 bis at Toulouse airport (Forward= 2886, sideway = 178, rotation = -30)Measurement at 40 km/hMeasurement at 13 km/h

Lab measurements on some receivers and associated ATOLL modelsTest settingILS receiver

R&S EVS 300AGC cut-off frequency: 9HzAGC filter order: 4Model parameters:LF band pass filters: 21HzLF band pass filter order: 5LF detection filter cut-off frequency: 8HzLF detection filter order: 2

MMR ThalesAGC cut-off frequency: 10HzAGC filter order: 4Model parameters:LF band pass filters: 4HzLF band pass filter order: 2LF detection filter cut-off frequency: 3HzLF detection filter order: 2

1Hz2Hz3Hz4Hz5Hz6Hz7Hz8Hz9Hz10Hz11Hz12Hz13Hz14HzNA

MMR CollinsAGC cut-off frequency: 3HzAGC filter order: 3Model parameters:LF band pass filters: 10HzLF band pass filter order: 3LF detection filter cut-off frequency: 6HzLF detection filter order: 2

1Hz2Hz3Hz4Hz5Hz6Hz7Hz8Hz9Hz10Hz11Hz12Hz13Hz14HzNA

Some resultsP6: TailForward= 1579m, sideway = 57m, rotation = 90

ATOLL simulation and measurements with DSNA receiver antenna (orange = raw data) and EVS200Disturbance amplitude:Disturbance amplitude with A380: T1 = 27 A, T2 = -31ADisturbance amplitude without A380 at same points: T1=-1A, T2=-1ADisturbance amplitude with A380 only: T1 = 28A, T2 = -30 A T1 = 26A, T2 = -29AT1 = 28A, T2 = -30A

Some resultsP6: TailForward= 1579m, sideway = 57m, rotation = 90

AXIS simulation with omnidirectionnal antenna.

Measurements with DSNA receiver antenna and EVS200Disturbance amplitude:Disturbance amplitude with A380: T1 = 27 A, T2 = -31ADisturbance amplitude without A380 at same points: T1=-1A, T2=-1ADisturbance amplitude with A380 only: T1 = 28A, T2 = -30 A T1 = 35A, T2 = -40AT1 = 28A, T2 = -30A

Some resultsP6: TailForward= 1579m, sideway = 57m, rotation = 90

NPPM simulation with omnidirectionnal antenna.

Measurements with DSNA receiver antenna and EVS200Disturbance amplitude:Disturbance amplitude with A380: T1 = 27 A, T2 = -31ADisturbance amplitude without A380 at same points: T1=-1A, T2=-1ADisturbance amplitude with A380 only: T1 = 28A, T2 = -30 A T1 = 36A, T2 = -38AT1 = 28A, T2 = -30A

Some resultsP6 bis: TailForward= 1579m, sideway = 83m, rotation = 90

IHSS simulation with DFS antenna.

Measurements with DSNA receiver antenna and EVS200Disturbance amplitude:T1 = 17A, T2 = -18ADisturbance amplitude with A380: T1 = 17 A, T2 = -20ADisturbance amplitude without A380 at same points: T1=-1A, T2=-1ADisturbance amplitude with A380 only: T1 = 18A, T2 = -19 A T1 = 18A, T2 = -19A

Some resultsP11 bis at 40 km/h : TailForward= 2886m, sideway = 178m, rotation = -30

ATOLL simulation and measurements with DSNA receiver antenna (orange = raw data) and EVS200Disturbance amplitude:Disturbance amplitude with A380: T1 = +6 A, T2 = +2ADisturbance amplitude without A380 at same points: T1=-1A, T2= 0ADisturbance amplitude with A380 only: T1 = 28A, T2 = -30 A T1 = +8A, T2 = +4AT1 = +7A, T2 = +2A

Some resultsP11 bis at 40 km/h : TailForward= 2886m, sideway = 178m, rotation = -30

AXIS simulation with omnidirectionnal antenna

Measurements with DSNA receiver antenna and EVS200Disturbance amplitude:Disturbance amplitude with A380: T1 = +6 A, T2 = +2ADisturbance amplitude without A380 at same points: T1=-1A, T2= 0ADisturbance amplitude with A380 only: T1 = 28A, T2 = -30 A T1 = +5A, T2 = +4AT1 = +7A, T2 = +2A

Some resultsP11 bis at 40 km/h : TailForward= 2886m, sideway = 178m, rotation = -30

NPPM simulation with omnidirectionnal antenna

Measurements with DSNA receiver antenna EVS200Disturbance amplitude:Disturbance amplitude with A380: T1 = +6 A, T2 = +2ADisturbance amplitude without A380 at same points: T1=-1A, T2= 0ADisturbance amplitude with A380 only: T1 = 28A, T2 = -30 A T1 = +3.5A, T2 = +3AT1 = +7A, T2 = +2A

Some resultsP11 bis at 13 km/h:TailForward= 2886m, sideway = 178m, rotation = -30

ATOLL simulation and measurements with DSNA receiver antenna (orange = raw data) and EVS200Disturbance amplitude:Disturbance amplitude with A380: T1 = +1 A, T2 = +2ADisturbance amplitude without A380 at same points: T1= 0A, T2= 0ADisturbance amplitude with A380 only: T1 = 28A, T2 = -30 A T1 = +3.5A, T2 = +4AT1 = +1A, T2 = +2A

Some resultsP11 bis at 13 km/h: TailForward= 2886m, sideway = 178m, rotation = -30

AXIS simulation with omnidirectionnal antenna

Measurements with DSNA receiver antenna and EVS200Disturbance amplitude:Disturbance amplitude with A380: T1 = +1 A, T2 = +2ADisturbance amplitude without A380 at same points: T1= 0A, T2= 0ADisturbance amplitude with A380 only: T1 = 28A, T2 = -30 A T1 = +5A, T2 = +4AT1 = +1A, T2 = +2A

Some resultsP11 bis at 13 km/h: TailForward= 2886m, sideway = 178m, rotation = -30

NPPM simulation with omnidirectionnal antenna

Measurements with DSNA receiver antenna and EVS200Disturbance amplitude:Disturbance amplitude with A380: T1 = +1 A, T2 = +2ADisturbance amplitude without A380 at same points: T1= 0A, T2= 0ADisturbance amplitude with A380 only: T1 = 28A, T2 = -30 A T1 = +3A, T2 = +3AT1 = +1A, T2 = +2A

The first step in this study was to select test points to measure the disturbances introduced by the A380 and its impact on the critical and sensitive areas.

This predefined set of test points has then be simulated by various ILS simulation tools in order to:Reduce the number of points to be measured to the most significant onesTo get some pre-measurement predictions in order to evaluate the prediction performances of the tools The measurements have then be analyzed to evaluate the impact of the A380 on the critical and sensitive areas. This was in fact the first objective of this study.

The second objective was to compare the measurements with the predictions of the modeling tools and evaluate the correlation between simulations and measurements

To simulate the output readings from an ILS receiver in presence of an ILS signal with interferences requires several steps.

Simulation of the radiation patterns delivered by the ILS as this has an impact on the incident signal on the obstacle.

Choose a method to simulate the propagation of electromagnetic waves and scattering on obstacles:

Several methods are available. Some of them (like the Method of Moments) give an exact solution of Maxwells equations.Some others are called asymptotic methods and are based on some approximations valid under some conditions.

One condition for the Physical optics is for example that the distance from the obstacles to the transmitter and to the receiver has to be greater than 2d2/l , with d one of the dimension of the object.Design a model of the object to evaluate (A380) that fits with the simulation method and represents the most critical parts involved in the scattering of electromagnetic waves

Simulate the radiation pattern of the receivers antenna Signals coming from different direction may be attenuated differently.

Receiver from different manufacturer may give other readout for the same ILS signal.

Measurement path and receiver speed have also to be simulated. As we will see later the speed plays an important role.

Several simulation tools have been used during this study.

I will now go trough all the steps of simulation in a little bit more details.

The reflected field from an object depends on the level of the incident signal which in turn depends on the radiation patterns of the ILS.

Here we have for example the radiation patterns from the 25 element Thomson array in use at runway 14RAt Frankfurt the runway 25L is setup with a 21/7 element array from THALES.

As the patterns from different ILSs are different the incident and so the reflected signals from an object will be different.A 3D model of the A380 is the most suitable object to use for simulating the impact of the A380 on the ILS signal. This model has to be subdivided into a set of triangles in order to apply the Method of Moments to calculate the scattered electromagnetic fields. The Method of Moments gives an exact solution of Maxwells Equation for propagation and scattering of electromagnetic waves.

For huge structures (like A380) the method requires however computers with huge processing power and storage capacities. The 3D model is not easy to handle and the computation time is very long (several hours for 1 scenario).

It was therefore interesting to see if simplified models (running on conventional PCs and requiring only a few minutes to calculate a scenario) could also lead to realistic results.The simplified method used in many ILS simulation tools is the Physical Optics. This asymptotic method gives an approximate solution of Maxwells equations and analytic solutions exist for rectangular plates as well as for cylinders.

The Navaids Performance Prediction Model from Ohio University uses several rectangular plates to model the A380.It is well known that the major impact from an aircraft on the ILS signal comes from his tail fin.

The Surface currents calculated with the Method of Moments confirms this. The red colored surfaces show the location of the highest surface current density which generate the reflected signal.

Simulating only this part of the aircraft may therefore give results in accordance with the measurements. The ILS simulation software ATOLL and AXIS are using this approximation to evaluate the interferences caused by the A380 on the ILS signal.The radiation pattern of the receiving measurements Antenna has also an impact of the amplitude of the interference as the reflecting signal may more or less be attenuated.

For the ground measurements 3 types of antennas were used. Some of the evaluated software can simulate the antenna patterns of the receiving antenna.The behavior of different receivers may lead to significant differences in the measurements for a given interference. Modeling the characteristics of the receiver is therefore required to compare simulations with measurements.

On these measurements we can see a significant difference between measurements made with 2 different ILS ground receivers. Amplitude of raw dates are les than half with the ARTUS receiver compared to the EVS200.Speed is also an important factor to evaluate and compare measurements with simulations.

Usually one expects an increase of the measured interference with decreasing speed. The 2 curves show the opposite. The filtered interference at 40 km/h is bigger than at 13 km/h.

As the direct and reflected signals are coming from different directions, it appears a frequency shift between those signals related to the Doppler effect. This Doppler shift can in some cases trigger capture effect in the receiver and lead to the mean deviation seen here at 40 km/h.

To get simulations in accordance with measurements this Doppler effect should be implemented in the simulation tools. Some lab measurements have been conducted by DSNA as well as by DFS to evaluate the behavior of some ILS receivers in presence of a strong reflection of the course signal.

The ILS signals from two generators have been added and fed to the receivers. One signal was simulating the direct signal for a receiver on runway center line (DDM=0A) and the second one a reflected signal. The level and the DDM from the reflected signal have been evaluated from real measurements in worst case situations.

The carrier frequency of the simulated reflected signal has then be changed gradually to simulate the Doppler effect.

The receiver model in ATOLL software has been adjusted to match the simulations with the measurements.The receiver model in ATOLL consists of an AGC filter, 2 LF band pass filters for the LF 90HZ and 150Hz tones and 2 low pass detection filters.

This slide shows the measurements and the corresponding simulation of the EVS300 from R&S