Egnos performance explained

EGNOS will provide enhanced performances over GPS according to four parameters: accuracy, availability, continuity and integrity. Although the concept of position accuracy is easy to understand, the other three notions are frequently misunderstood. They are defined as follows by the system requirements:

• Integrity
Integrity relates to the trust which can be placed in the correctness of the information supplied by the Navigation System, it includes the ability of the system to provide timely warnings to the user when the system or data provided by the system should not be used for navigation.


• Continuity
Continuity of Navigation service is defined as the probability that the accuracy and integrity requirements will be supported by the Navigation System throughout a flight operation or flight hour given that they are supported at the beginning of the flight phase and that the flight operation is initiated and predicated to be supported all along the flight phase. Satellite outages predicted at least 48 hours in advance of the outage do not contribute to a loss of continuity.


• Availability
Availability of the Navigation Service is the probability that the Positioning service and the Integrity monitoring service are available and provide the required accuracy, integrity and continuity performances. Availability is computed, at any point within the service volume, as the percentage of the time during which the service is available over the lifetime of the system, taking into account all the outages whatever their origins. The service will be declared available when accuracy, integrity and continuity requirements are estimated to be met.