EGNOS Approach with Vertical guidance state investigation

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EGNOS APPROACH WITH VERTICAL GUIDANCE STATE INVESTIGATION

Kalagireva Karina Leonidovna

Technical University of Sofia, Bulgaria

Department of Aeronautics

PhD student

Abstract

This report presents the investigation of the state of EGNOS Approach with Vertical guidance for Europe. EGNOS performance parameters are described in terms of accuracy, integrity, availability and continuity. The established results confirm the need for the EGNOS service and its availability in Europe.

Keywords: accuracy, Approach Procedure with Vertical Guidance, Availability, continuity, European Geostationary Navigation Overlay Service, European Satellite Services Provider, Integrity

Introduction

EGNOS (European Geostationary Navigation Overlay Service), operated by the European Space Agency, is the wide-area differential system SBAS (Space Based Augmentation System) that is used to improve the accuracy in determining the coordinates of the objects.

The European SBAS has been deployed to provide regional satellite-based augmentation services to aviation, maritime and land-based users in Europe. [1]

EGNOS helps to increase passenger safety thanks to allowing instrument approach procedures that are safer than non-precision approaches. For airlines it helps to make fewer delays, diversions and cancellations due to bad weather conditions or poor visibility at airports that are not equipped with ground-based navigation aids. For such airports EGNOS increases capacity as separation between aircrafts can be reduced; increases accessibility as planes can land even in bad weather/poor visibility conditions; reduces costs compared to the installation and maintenance of ground-based navigation aids as EGNOS only requires an approach procedures for the runway. [2]

Fig. 1 EGNOS service area map

egnos guidance accuracy europe

EGNOS provides a cost effective alternative equivalent to ILS CAT I, offering similar performance without the need for infrastructure installation and maintenance. It is a very valuable navigation aid mainly to small and medium-sized airports, increasing safety and accessibility to those aerodromes. [3]

Composition, main functions and parameters of EGNOS

The EGNOS system includes 3 major segments: space, ground and user. The space segment consists of geostationary satellites and its main function is the propagation of the EGNOS signal. The ground segment is a network of ground stations, with the aid of which the production of the EGNOS signal and the management of the whole system are observed. The user segment represents receivers located on objects that use the services of EGNOS. [4]

Currently EGNOS offers full coverage (APV-I 99%) over Austria, Belgium, Denmark, France, Germany, Luxemburg, Netherlands, Slovenia, Switzerland, Croatia, Bosnia and partial coverage over Czech Republic, Finland, Hungary, Ireland, Italy, Poland, Portugal, Slovakia, Spain, Sweden, United Kingdom, Norway, Montenegro and Serbia.

The EGNOS coverage area is Western Europe, but could be readily extended to include other regions within the broadcast area of the geostationary satellites such as Africa, Eastern European countries and Russia. EGNOS is the first element of the European satellite-navigation strategy and a major stepping-stone towards Galileo, Europe's own future global satellite navigation system.

Using EGNOS for instrument approaches can bring the decision height down to as low as 250 feet (about 75 meters), which is close to ILS Cat I. This means that the pilot can take the aircraft down “blind”, without visual contact to the ground, to as low as 250 feet above ground. A future version of EGNOS will allow for 200ft minima which is equivalent to Instrument Landing System Cat I. [5]

Next table shows, for each country:

- The number of airports with LPV procedures, as well as total number of LPV procedures;

- The number of airports with APV Baro procedures authorized to be flown with EGNOS vertical guidance as well as the total number of APV Baro procedures. [6]

Table 1 LPV & APV Baro procedures published per country (December 11, 2014)

Investigation of the state of EGNOS Approach with Vertical guidance for Europe given by European Satellite Services Provider

EGNOS APV-I Availability

It is defined as the percentage of epochs in a month/in the period in which the Protection Level is below Alert Limits for this APV-I service (HPL<40m and VPL<50m) over the total period.

Figure 2 presents the EGNOS APV-I Availability for the period April 2012 - March 2013 for Europe:

Fig. 2 EGNOS APV-I Availability, April 2012 - March 2013

Figure 3 presents the EGNOS APV-I Availability for May 2014 for Europe:

Fig. 3 EGNOS APV-I Availability, May 2014

Figure 4 presents the EGNOS APV-I Availability for December 2014 for Europe:

Fig. 4 EGNOS APV-I Availability, December 2014

The availability of the system for APV-I for Sofia (for example) for the period April 2012 - March 2013 reaches 99.6%. The availability of the system for APV-I for Sofia on May 2014 reaches 99.9% and on December 2014 reaches 99.6%.

EGNOS APV-I Continuity Risk

It is defined as the result of dividing the total number of single continuity events using a time-sliding window of 15 seconds by the number of samples with valid and available APV-I navigation solution. A single continuity event occurs if the system is available at the start of the operation and in at least one of the following 15 seconds the system becomes not available.

Figure 5 presents the EGNOS APV-I Continuity for the period April 2012 - March 2013 for Europe:

Fig. 5 EGNOS APV-I Continuity Risk, April 2012 - March 2013

Figure 6 presents the EGNOS APV-I Continuity for May 2014 for Europe:

Fig. 6 EGNOS APV-I Continuity Risk, May 2014

Figure 7 presents the EGNOS APV-I Continuity for December 2014 for Europe:

Fig. 7 EGNOS APV-I Continuity Risk, December 2014

APV-I continuity between April 1^st 2012 and March 31^st 2013 is reported as the number of single continuity events in a time-sliding window of 15 seconds over the total number of available samples in the period. The result is presented as the probability per 15 seconds of occurrence of one discontinuity event.

The continuity of the system for APV-I for Sofia (for example) for the period April 2012 - March 2013 is about 2.5Ч10^-4. The continuity of the system for APV-I for Sofia on May 2014 is about 10^-4 and on December is about 5Ч10^-4.

EGNOS APV-I Integrity Event

It is defined as an event when the Navigation SE (System Error) is greater or equal to the corresponding PL (Protection Level) for APV-I.

No integrity event has been identified for any receiver of the monitoring network for the period April 2012 - March 2013, for May 2014 and for December 2014.

Safety Index is defined as the relation between Navigation System Error versus Protection Level (assuming PA algorithms to compute xNSE and xPL) for each second. In case of ratio xPE/xPL is over 1; it indicates that a Misleading Information situation has occurred.

Figures 8 and 9 provide the histogram for HSI (Horizontal Safety Index) and VSI (Vertical Safety Index) corresponding to the RIMS sites located inside the APV-I for the period April 2012 - March 2013 for Europe.

Fig. 8 EGNOS APV-I Horizontal Safety Index, April 2012 - March 2013

Fig. 9 EGNOS APV-I Vertical Safety Index, April 2012 - March 2013

The Horizontal and Vertical Safety Indexes remain below 0.4 for all stations throughout the whole period, which represent a very good integrity margin.

Figures 10 and 11 provide the histogram for HSI and VSI for each second when accumulating measurements from the different EGNOS stations of Europe for May 2014:

Fig. 10 EGNOS APV-I Horizontal Safety Index, May 2014

Fig. 11 EGNOS APV-I Vertical Safety Index, May 2014

HSI and VSI are <0.75 so there is no potential possibility for Misleading Information. These histograms have considered that Protection Level is below APV-I Alarm Limit.

Figures 12 and 13 provide the histogram for HSI and VSI for each second when accumulating measurements from the different EGNOS stations of Europe for December 2014:

Fig. 12 EGNOS APV-I Horizontal Safety Index, December 2014

Fig. 13 EGNOS APV-I Vertical Safety Index, December 2014

HSI and VSI are <0.75 so there is no potential possibility for Misleading Information. These histograms have considered that Protection Level is below APV-I Alarm Limit.

EGNOS APV-I Accuracy

It is reported as the 95th percentile of the Horizontal and Vertical Navigation System Error over the month, at the monitored sites when the APV-I service is available (HPL<40m and VPL<50m).

The APV-I accuracy values in meters for all stations in Europe for the period April 2012 - March 2013: HNSE 95% - 1.3 m, VNSE 95% - 2.3m.

The APV-I accuracy values in meters for Sofia (for example) station for May 2014: HNSE 95% - 1.2 m, VNSE 95% - 2.4m, 99.97% of samples with APV-I service available.

The APV-I accuracy values in meters for Sofia (for example) station for December 2014: HNSE 95% - 1.1 m, VNSE 95% - 2.1m, 99.71% of samples with APV-I service available.

These results represent a very good level of accuracy for Europe. [7] [8] [9]

Conclusion

The availability of EGNOS to aviation means that aircrafts will be able to use satellite technologies to establish their vertical positioning during approaches. The established results support the claim: nowadays EGNOS performance is stable with high quality of the accuracy and integrity.

References

1. Суницкий Е. Широкозонные системы спутниковой дифференциальной навигации, Геопрофи, 2005.

2. Международный комитет по глобальным навигационным спутниковым системам (МКГ), Oбсуждениe возможностей применения глобальных навигационных спутниковых систем (ГНСС) в интересах людей во всем мире, 2008.

3. ESA, The present - EGNOS, Documentation, 2011.

4. Василев Б., Василева Б. EGNOS - спътникова навигация за Европейското въздушно пространство, София, 2012.

5. EGNOS for Aviation - What is a LPV procedure? What benefits EGNOS LPV bring to current navigation aids?

6. ESSP, EGNOS Bulletin, 2014.

7. ESSP MPR - European Satellite Services Provider, Monthly Performance Reports, May 2014.

8. ESSP SAS - European Satellite Services Provider SAS, Service Provision Yearly Report, April 2012 - March 2013.

9. ESSP MPR - European Satellite Services Provider, Monthly Performance Reports, December 2014.

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