The European Geostationary Navigation Overlay
Service (EGNOS)
GNSS-1 OPERATIONAL
VALIDATION
EGNOS COULD BRING PEACE AND QUITE
TO THE CAP D’ANTIBES
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The European Geostationary Navigation Overlay Service (EGNOS)
EGNOS, the European Satellite-Based Augmentation System (SBAS) to GPS, is currently under development and is expected to be in operation by 2004. The EGNOS system provides additional signals to users of satellite navigation services, broadcast through geostationary satellites guaranteeing the integrity of GPS so that it can be used in support of safety-of-life services such as civil aviation (fig 1).
Figure 1. EGNOS System Architecture
EGNOS is designed, among other things, to meet the requirements of Approach procedures with Vertical Guidance, also known as LNAV/VNAV (Lateral/Vertical RNAV Approach) or APV.
EUROCONTROL, as a part of its commitment to the European Tripartite Agreement with the Commission of the European Union and ESA (European Space Agency), is responsible for the co-ordination of the operational validation of EGNOS for Civil Aviation.
Further information on EGNOS can be found on the ESA web-site.
Operational validation includes all activities that will demonstrate that EGNOS is ready to be implemented to support the flight operations for which it is intended. The operational validation activities are co-ordinated through a group known as the ‘GNSS-1 Operational Validation (GOV) Working Group’ (fig 2), chaired by EUROCONTROL and primarily composed of European Air Traffic Service Providers intending to offer navigation services based on EGNOS. The GOV group is performing various activities that will support the implementation of EGNOS services for Civil Aviation in European airspace. One important activity within the GOV is to establish the type of operations that will be supported by EGNOS and based on this to develop an operational concept for the use of EGNOS by Civil Aviation in Europe.
Figure 2. EGNOS and GOV schedule
Experimental work plays a crucial role within the work carried out by the GOV. The current ‘Early Trials’ activities focus primarily on gathering experience with EGNOS using the EGNOS System Test Bed (ESTB) (fig 3). This includes the development of prototype tools for static and onboard data collection and evaluation.
Combining both technical and operational activities, EUROCONTROL, in co-operation with ESA and the French DGAC, conducted flight trials at Nice in September 2001 that demonstrated how EGNOS could facilitate curved approaches, improving safety and reducing aircraft noise for local inhabitants.
Further information on GOV activities can be found at the SBAS web-site
EGNOS COULD BRING PEACE AND QUITE TO THE CAP D’ANTIBES
Today, aircraft have a choice when approaching Nice airport: they either choose a visual approach along the Cap d'Antibes peninsula followed by a sharp unguided turn - a complex manoeuvre; or, under poor visibility, they choose an ILS Cat-I approach straight over the peninsula - raising many noise complaints from local residents. Hence, Eurocontrol considered this to be an ideal opportunity to test an EGNOS-based curved approach with vertical guidance as part of its operational validation activities.
Figure 3. EGNOS System Test Bed Architecture
Working together with the French DGAC, they designed a bespoke curved approach procedure for Nice based on draft and existing design criteria (Fig 4). There are curves in this that can only be flown by aircraft with state-of-the-art Flight Management Systems (FMS), and vertical guidance is required all along the approach path from a high integrity navigation aid such as EGNOS.
This approach was tested initially using a commercial transport aircraft simulator. Two scenarios were studied: firstly, GPS alone with baro-altimeter to capture the ILS that is then used to land the aircraft; and secondly, EGNOS for the complete procedure. During the tests, it quickly became apparent that the former was not possible because the final straight approach was too short to acquire the ILS. Only a navigation aid providing continuous guidance along the approach would allow the Nice procedure to be flown.
Figure 4. Curved approach procedure to Nice based on SBAS draft criteria
The flight tests took place on 26th and 27th September 2001 using NLR's Cessna Citation II research aircraft (fig 5). EGNOS was investigated in two different ways: firstly by applying the ESTB position and integrity data to support flying curved approach procedures; and secondly, by providing ILS look-alike ESTB guidance to fly the standard straight-in approach to Nice straight over the Cap d'Antibes.
Figure 5. NLR's Cessna Citation II research aircraft
The results were processed using real-time kinematic GPS as the truth reference track (Fig 6). From these, it was concluded that the ESTB met the demanding integrity and accuracy requirements for APV II precision approach. Most importantly, the pilots themselves were very complimentary … "Basically it was easy to fly the curved approaches using guidance from the ESTB … in general we were very impressed with the guidance from the ESTB system".
Figure 6. Ground Equipment used for truth reference computation
EGNOS will facilitate such curved approaches, bringing benefits to pilots and the environment. When EGNOS is fully operational in 2004 it should be possible for suitably equipped aircraft to choose a controlled curved-approach, improving safety and reducing aircraft noise for local inhabitants (fig 7).
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Figure 7. Current (left) and SBAS (right) LAmax noise contours (dBA)
EGNOS Trials at Nice Airport – Noise Impact Study
For further information please contact:
Rick Farnworth Richard.Farnworth@eurocontrol.int
Santiago Soley Santiago.Soley@eurocontrol.int
