EGNOS Aviation Services Evolution
Background & Objectives
The European Commission is defining the long term evolution of the EGNOS programme beyond the EGNOS Service Release of EGNOS V3 currently defined. Evolutions shall support the implementation of safer and more efficient aviation operations. In this sense, further evolutions of EGNOS services for aviation safety beyond 2025 could take any of the following three directions:
- Enlarge the provision of EGNOS services to Communication Navigation Surveillance (CNS) and Air Traffic Management (ATM) beyond navigation, notably to address surveillance (ADS-B) and possibly support timing services for communication systems;
- Provide additional features to increase the robustness against external intentional or unintentional threats/attacks to the EGNOS navigation service, for instance by adding authentication to GNSS signals or ad hoc features at antenna and receiver level;
- Enhance the navigation, positioning and/or timing performance provided at user level, for instance by improving the vertical position accuracy and the time-to-alert to enable supporting Cat-II approach procedures.
The aims are to analyse and define the reasons motivating evolutions along those three axes beyond 2025, determine constraints and pre-requisites, and assess the added value to end users. The analysis shall consider each area separately and determine under what condition it would be beneficial for the programme to implement these services. The analysis shall focus on:
- Identifying user requirements for each of these new services and how they translate into service requirements for EGNOS;
- Defining the associated regulatory constraints and safety analyses required before the service can be implemented operationally;
- Analysing the added value for aviation end users and defining how the service could be provided, to enable a programmatic decision on which service should be implemented as a priority.
Work performed & results
Consultation of European ATM community allows the identification of future applications that would benefit from EGNOS V3 services. These applications are:
- Enhanced A-SMGCS application: ADS-B is used to enhance the surveillance quality (by providing an additional surveillance means) at airports already equipped with A-SMGCS. This solution allows improving the A-SMGCS alerts and routing function (e.g. Follow the green function) or may also enable the implementation of additional alerts.
- Alternative A-SMGCS applications: ADS-B is used as a sole means to provide an alternative surveillance means with the required performances for an “ASMGCS like”, i.e. an A-SMGCS with possibly a reduced number of alerts or functions.
- SURF-IA (Enhanced Traffic Situational Awareness on The Airport Surface With Indications and Alerts): it consists in providing flight crew with visual awareness on the airport moving map display and indications and alerts (aural and on devices) about situations where collision hazard exists or a collision appears imminent.
- SURF-A consists in providing alerts to the pilot with respect to surrounding traffic during runway operations to prevent collision on the runway. SURF-A is similar to SURF-IA but does not include the use of a Cockpit Display of Traffic Information (CDTI) and the provision of indication.
- EGNOS Vertical reference service: EGNOS is used as a new altitude reference system; geodetic altitude is used instead of barometric pressure measurements to calculate the altitude.
- Special Authorisation (SA) CAT I operations: SA CAT I approaches are introduced as an operational credit to extend the instrument segment of a CAT I approach to allow CAT I operations down to a DH of 150 ft, subject to holding specific approval from the competent authority.
- CAT II operations: Equivalent to current CAT II operations.
In addition, assessment of constraints to implement a SBAS authentication service in the aviation context has been performed.
Consolidated SBAS requirements
No explicit requirements (e.g. in term of accuracy, integrity, availability) have been defined so far for the ADS-B surveillance source for alternative or enhanced ASMGCS applications. Consequently tentative ones (e.g. for accuracy) have been proposed from a comparison with the ones from other existing means of surveillance. For SURF-IA, ADS-B requirements have been defined in the RTCA standard and for SURF-A, ADS-B requirements have been proposed by the manufacturer as part of the SESAR project. So far, the most stringent requirements concerned the accuracy of the position for which NACp equal to 10 or 11 would be required (i.e. an accuracy < 10m or 3m). For the EGNOS Vertical reference service, a set of requirements have been proposed based on stakeholder consultations. Lastly, Egis proposed requirements for SA CAT I with accuracy requirements obtained by linearization of ILS CAT I performance at a DH of 150 ft, and HAL/VAL requirements derived by scaling the accuracy by 2.5. The presented CAT II requirements are based on equivalency of ILS CAT II requirements for information purposes only. However, it is recommended to derive SBAS CAT II requirements considering SBAS characteristics and its integration within the aircraft.
The preliminary safety analysis that were conducted (both for the use of the same source of position for navigation and surveillance, and on beyond CAT I operations) indicated that the use of EGNOS for future service does have major impact on the EGNOS V3 system in general (i.e. ground system and receivers which are already DAL B certified).
Concerning the authentication service, the use of the authentication may increase the likelihood of loss of EGNOS service. SBAS authentication scheme should be designed to limit this increase. Moreover, the authentication function would need to be designed in a way it ensures high levels of availability and continuity (since it contributes to the loss of EGNOS service).
From a service point of view, the new services (i.e. EGNOS-enabled ADS-B services and vertical reference service) could be categorised as a constituent service for Navigation and there is no need to have a different service provider.
Similarly, for authentication service, no specific advantage has been identified for using an operator different from the SBAS one.
The provision of the new services (i.e. EGNOS-enabled ADS-B services and vertical reference service) would oblige the EGNOS Service Provider (ESP) to complete a safety assessment for the functional change but it would not require them to set up new processes for safety oversight and safety performance monitoring.
The definition of specific Service Level(s) (SL) of the EGNOS Safety of Life service associated with the new services may be required but this would need to be confirmed by airworthiness authorities and the EGNOS service provider.
Costs and Benefits analysis
For ADS-B operations and beyond CAT I operations, the benefits have been calculated per segment considering small, medium and large/very large airports and the average number of movements on these airports and a typical aircraft per type of airport for the airspace user perspective.
Benefits associated with A-SMGCS applications, have been quantified based on:
- For Airspace users, fuel savings resulting from taxitime optimization;
- For ANSP, safety benefits associated with continuity of the revenue that could result from a decrease of the impact on incident on the continuity of airport activities.
Benefits for both SA CAT I and SBAS CAT II services have been quantified based on:
- For ANSPs, a reduction of the loss of revenues due to the capacity gained during adverse weather conditions;
- For Airspace Users, a reduction of delay and diversion costs.
For the vertical reference service, the benefits have been quantified for the ECAC traffic and aircraft fleet only, in term of fuel savings for airspace users and increased capacity for ANSP, making distinction between oceanic and continental traffic.
Further insight into the results are available in the project Final Report: EASE Final Report
Enhanced A-SMGCS operations
The implementation of the Enhanced A-SMGCS solution will be highly beneficial for Large and Very large airports as it is expected to increase the taxi time optimisation of 3% compared to their actual performance.
For the implementation of Alternative A-SMGCS for medium size airports, the taxi time improvement benefits are not sufficient to balance implementation costs and the return on investment will occur instantly if a major incident impacting 50% of their operations is avoided thanks to the solution implementation.
Added value of the situational awareness SURF A/ IA applications, would be relatively small and difficult to assess at airports which are already equipped with A-SMGCS (Enhanced or Alternative).
Vertical reference service
There are both qualitative and quantitative potential benefits that would support and enable the air traffic growth and would contribute to both safety of operations and improvement of cost-efficiency. Enough incentives are required to obtain the stakeholders buy-in
SBAS SA CAT I operations
The economic benefits of implementing SBAS SA CAT I are mainly derived to the reduction of the number of aircrafts diverted to other airports in low visibility conditions.
SBAS CAT II
In CAT I airports, the economic benefits may not compensate the required investment, especially in small and medium size airports, which are the typical size of CAT I airports. In this case CAT I airports would probably prefer to invest in SA CAT I implementation (if the airport would absolutely need CAT II for their operations, they would probably have already invested in an ILS CAT II/III).