Nicola Cortesi, Michele Ducci, Alessandro Nobiletti, Alberico Parente

> IDS S.p.a. - Airnavigation and Navaid Division

Marco Bucci, Oberdan Rancitelli

> ENAV S.p.a. -- Servizi Tecnici, Ingegneria

**THE MIXED USE OF FLIGHT INSPECTION AND COMPUTER SIMULATION: THE ENAV
EXPERIENCES WITH AIRNAS ®**

####### June , 2002

##### ABSTRACT

Nowadays advance in computational electromagnetic and computer science
has given the possibility to inspect the navaids installations
constraints and modification via computer modeling. ENAV S.p.a. was one
of the leading organizations in the above mentioned field, starting
it\'s cooperation with IDS S.p.a. since 1994.

During these years IDS and ENAV experienced many common activities in
the field of navaids siting design: since 1994 the nearly 100% of new
navigations aids were installed with the help of the IDS computer
modeling tools of the AIRNAS ® framework.

The AIRNAS ® framework was developed by IDS S.p.a. in order to execute
the EMC analyses requested by its customers to determine the expected
radioeletric performances of the new navaids equipments taking into
accounts the interactions with surrounding environment (man made
obstacles, terrain and other Tx/Rx equipments) before the system
installation. In 2000 ENAV S.p.a. decided to supply its engineering
division with a its own computational capability acquiring from IDS
S.p.a. an AIRNAS ® system. The following paper will describe some of the
experiences accumulated during the past years of the common IDS and ENAV
collaboration.

##### 

##### THE AIRNAS ® HISTORY

The development of the AIRNAS ® system began between the late '80s and
early '90s when IDS s.p.a. proposed to ENAV S.p.a. (named AAAVTAG at
that time) the use of its prediction tools (developed and used since the
1982 in the navy EMC analysis field) for the solution of the e.m.
problems related to the installation and the preservation of Ground/Air
TLC systems, radio navigation aids and radars.

The collaboration with ENAV started with a benchmark project: the e.m.
characterization of the GP equipment of the Napoli/Capodichino airport
(ICAO code LIRN, IATA code NAP). ENAV supported IDS with the data
relevant to the airport area, the technical data of the installed
equipment and the flight checks of that equipment.

IDS s.p.a. executed the required numerical simulations, and was able to
demonstrate the capabilities and the accuracy of its prediction tool
that was named EMACS (ElectroMagnetic Airport Control and Survey). Since
that trial activity the EMACS system was used as an IDS internal tool
for the e.m. analysis and design of the installation of:

-   10 VOR/DME

-   6 ILS

-   12 ATC radar

-   6 SMR radars

-   3 weather radar

-   10 Air/Ground TLC

-   6 MLS

In 1993/1994 IDS s.p.a. granted from ENAV s.p.a. a contract for an
automated Sw system for the instrument flight procedures design: the
SIPRO system. The evolution of the SIPRO system was named FPDAM ® and is
currently in use by more than 12 CAAs all over the world.

In the late '90s the IDS Airnavigation and Navaid Division was in charge
of a powerfull e.m. tool (the EMACS system) and of a quite successful
product for the instrument approach procedures design and airspace
management (the FPDAM ®): the were the conditions for a more in depth
integration of FPDAM ® and EMACS, and so it was created the AIRNAS ®
system as a multi disciplinary modular design environment (Framework)
based on CAD and simulation techniques capable of concurrently dealing
with problems related to:

-   the different phases of air navigation design (e.g.: en-route,
    landing, missed approach, etc.);

-   data relevant to the airspace management (e.g.: FIR, ATM, ATZ,
    operative sectors, routes, navaids, ...)

-   the various tasks involved in system choices and performance
    evaluation of Navaid and ATC systems.

***AIRNAS ®*** is composed by:

-   an aeronautical Data Base, a GIS (compliant with aeronautical
    requirements);

-   a 3D CAD (fully integrated to the GIS);

-   a module library implementing the **ICAO-PANS-OPS**, the **US
    TERPS** and **NATO STANAG APATC 1A** design criteria

-   a library of electromagnetic simulation tools to evaluate the
    interactions between R/Tx systems and the nearby environment.

***AIRNAS ®*** is conceived to be capable of assisting both the AIS
designer and the Navaid-ATM/ATC designer

As depicted in the conceptual scheme of Figure 1, ***AIRNAS ®*** is
composed of the following major blocks:

1.  **FPDAM ®:** the Flight Procedure Design and Airspace Management is
    a three-dimensional CAD tool that provides an interactive
    environment for Aeronautical Flight Procedures design, Air Space
    management and Air Navigation using the new GPS based concepts.
    **FPDAM ®** takes into account all factors affecting flight
    procedure performance (airdrome terrain model, artificial obstacles,
    type of aircraft, ICAO Rules, GNSS satellite constellation etc.),
    within an interactive environment capable of ensuring a tight
    control on the system configuration and on all elements and design
    criteria related to flight safety issues;

2.  ***EMACS***: ElectroMagnetic Airport Control and Survey is a set of
    validated electromagnetic 3D modelling and simulation tools, capable
    of coping with EMC (ElectroMagnetic Compatibility issues and EMI
    ElectroMagnetic Interference problems in airport and air navigation
    site scenarios. The modelling functionality (including terrain
    models, obstacles, interfering system, ground and airborne navaid
    equipment characteristics etc.) allows an expert user to model the
    propagation real phenomena taking place within a complex e.m.
    airport scenario where signals (VOR, DME, ILS, ATC Radar, GPS
    systems) interfere with artificial or natural obstructions;

3.  ***VESAS***: Virtual Electromagnetic Satellite nAvigation Simulation
    system is an environment currently under development (planned for
    3^rd^ Q 2002) ehich is devoted to solve the major problems related
    to the aeronautical Satellite navigation. VESAS is composet of two
    working tools:

-   **SAPET** (Satellite navigation Performance Evaluation Tool) is a
    simulation tool devoted to analyse the GNSS satellite constellation
    (GPS, GLONASS and geostationary), and is able to assess parameters
    such as satellite visibility (on fixed points, flight procedures and
    geographical area), DOP, ...

-   **GEMS** (GNSS EM virtual flight Simulation, currently under
    development) is a set of tools devoted to assess the electromagnetic
    characteristics of the satellite signals such as field strength,
    multipath, EMI, ...

4.  ***Aeronautical Data Base*** for archiving all design relevant data
    and all elements concurring to the safety of flight procedures and
    Air traffic control;

5.  ***AIRNAS ® Cartographic and modeling tool*** to create the 3D
    models of the aeronautical environment

##### EXAMPLE CASES

**1.- An ILS/LLZ case**

The LLZ equipment of the Venezia/Tessera international airport (ICAO
code LIPZ, IATA code VCE) experimented some problems that drove its
signal very close (or slightly beyond) to the Cat. III course structure
max. ratings. This problem was solved by means of an antenna
recalibration plus flight checks, but no one was able to demonstrate if
that problem was in way related to the construction of a new hangar
within the airport area. The AIRNAS ® system, acting on a virtual model
of the reality, was able to analyse the multipath contribution of each
airport element separately from the other ones. The whole airport model
was set-up and simulations were carried on in order to compare the
measured data (both along the runway axis with a van and along the
approach path with a ENAV S.p.a. flight inspection aircraft) with the
computed one (see Figure 2). The goal of this simulation activity was
the measure of the degree of accuracy of the numerical model of the
airport: the numerical model of the Venice airport was judged good
enough for the porpoise of the commissioned task. Starting from this
model, two simplified airport models were created: the first one was the
same of the complete one with the new hangar removed and the second one
was only composed by the new hangar as it were the only building within
the airport area.

The DDM curve relative to the first model showed only slight differences
from the one taking into account the whole airport, and the DDM curve
relative only to the new hangar showed scattering contributions of the
LLZ signal in an area not relevant to the LLZ operations.

**2. A VOR case**

Many application examples of the AIRNAS/EMACS system can be cited, among
them there is the Torino/Caselle (ICAO code LIMF, IATA code TRN)
international airport case. This was the installation of a new
equipment, so it was not possible a cross-check with flight measurements
as in the case of the Venice LLZ. In this case were executed a
sensibility analysis to inspect the stability of the solution (i.e. if
the bearing error curve variation to parameters modification is many
different parametric analyses varying some elements such as:

The airport infrastructures position

-   The airport infrastructures dimensions

-   The materials constituting the infrastructures

-   The numerical techniques used for the simulation of the VOR signal
    interaction with the surrounding environment.

All those test showed minimum changes in the VOR signal parameters
(essentially the signal strength and the bearing error), and this is the
proof of a stable and then reliable solution.

Some months after the execution of those e.m. analyses, the execution of
the commissioning flight check on the installed equipment made possible
a comparison between measured and computed data (as shown in Figure 3),
showing a good degree of agreement.

**3. A DME case**

When IDS started the design of the Sw module dedicated to the evaluation
of the multipath effects on the DME signal, it was decided to ask for
the support of the Avionics Engineering Center of Ohio University in
order to set-up some test cases to test and validate that new module.

Within this frame AEC selected two measurement set-up which were used
for such a purpose (see Figure 4 and Figure 5), and IDS used its Sw
module in order to model the multipath effects on that equipments.

**4. A RADAR case**

The last example of the use of the AIRNAS/EMACS tool for the radar e.m.
analysis is the Lamezia Airport case ().

ENAV s.p.a. is planning the installation of a new APP radar within the
Lamezia airport area, so it was decided to perform the e.m. feasibility
analysis of the installation of this equipment within the frame of the
on-the-job training of the ENAV personnel to the use of the AIRNAS ®
tools.

As shown in Figure 6 and in Figure 7 it was possible to asses the:

-   Antenna pattern distortion due to the interaction with the airport
    infrastructures

-   The radar radio coverage taking into account of the presence of both
    site obstacle and the terrain around the antenna location.

The radar analysis module is also able to evaluate the minimum safe
altitude at which execute the commissioning flight checks taking into
account of both the radio coverage volume and the aircraft's obstacle
clearance for a safe flight.

##### CONCLUSIONS

The AIRNAS ® tools is a system developed for:

-   The design of instrument flight procedures and the management of the
    airspace data (AIRNAS/FPDAM ®)

-   The analysis (by means of computational electromagnetic techniques)
    of the radioelectric performance of TLC equipments, radionavigation
    aids and radar systems (AIRNAS/EMACS).

This system has a close interaction with the instrument flight
measurement data because:

-   AIRNAS ® uses those data in order to validate the numerical models
    of the environment around the antenna under analysis;

-   Increase the effectiveness of the commissioning flight inspection of
    new equipments because the numerical analysis is able to highlight
    the areas of the out-of-tolerance of the signal of that equipment;

-   Reduce the need (or nearly eliminate) of use portable equipments in
    the case of radionavigation aids installation in critical sites;

-   Increase the safety of the flight during the equipment inspection
    tanks to the ability of compute the obstacle clearance along with
    the volume of operation of the equipment under check.

##### ACKNOWLEDGEMENTS

The authors would express their sincere thanks to Capt. Giancarlo
Gozzini and to all the other guys from the Reparto Radiomisure ENAV
S.p.a. for their support during the past years of cooperation.

##### REFERENCES

1.- ICAO Annex 10 to the Convention on International Civil Aviation

2\. ICAO Doc. 8071 "Manual on Testing of Radio Navigation Aids"

3\. FAA Doc. 8200.1A "United States Standard Flight Inspection Manual"

4.- ICAO Doc. 8168: "Procedures for Air Navigation Services -- Aircraft
Operations (PANS-OPS)"

5.- Lettera di Ordinazione ENAV n. AV/AOT/DAO/2151 del 11/04/2000:
Realizzazione di un sistema di seconda generazione (AIRNAS 1) per la
progettazione, validazione e pubblicazione delle procedure strumentali
di volo e della gestione degli spazi aerei, anche nel contesto della
navigazione satellitare (GNSS)

6.- Avionics Engineering Center: Technical Memorandum OU/AEC
01-05TM00/AOSTA-RNAV/492/321 "Assessment of Ingegneria Dei Sistemi
Distance Measuring Equipment Multipath Model", February 2001

7.- Articolo ESA su ILS

##### FIGURES

![](media/image1.png){width="3.5145833333333334in"
height="1.7805555555555554in"}

Figure 1: Conceptual scheme of the AIRNAS ® framework

![](media/image2.wmf){width="3.3618055555555557in"
height="2.0854166666666667in"}

Figure 2: Venezia/Tessere LLZ DDM along the runway centerline

![](media/image3.png){width="3.3465277777777778in"
height="2.592361111111111in"}

Figure 3: Computation/Measurement comparison of Torino/Caselle Airport
DVOR bearing error

![](media/image4.wmf){width="3.509027777777778in"
height="2.467361111111111in"}

Figure 4: IDS S.p.a. Computed DME error

![](media/image5.wmf){width="3.411111111111111in"
height="1.5194444444444444in"}

Figure 5: DME error measurements made by Avionics Engineering Center
(Ohio Univ.)

![](media/image6.png){width="3.2125in" height="2.4090277777777778in"}

Figure 6: Example Lamezia APP radar antenna gain aberration prediction

![](media/image7.png){width="3.2131944444444445in"
height="3.2069444444444444in"}

Figure 7: Example of Lamezia radar coverage prediction