Due to the low elevation of the EGNOS (European Geostationary Navigation Overlay Service) satellites, their signal is difficult or sometimes impossible to receive in certain regions. Many present and also future applications require a high accuracy and also a high reliability of the position determination, which can easily be performed by EGNOS. But if the EGNOS signal cannot be received, the requirements of those applications can no longer be satisfied. Therefore, EGNOS TRAN evaluated various technical methods to broadcast the EGNOS signal via terrestrial networks, like GSM/GPRS, Loran-C or Ground Regional Augmentation System (GRAS).

In the frame of the EGNOS TRAN (European Geostationary Navigation Overlay Service - Terrestrial Regional Augmentation Networks) civil aviation application, an EGNOS reference station (ERS) was installed at Kiruna airport, north of Sweden. The ERS interfaces with a CNS (Communication Navigation and Surveillance) station from GRAS (Ground Regional Augmentation System) to broadcast the EGNOS message by means of a VHF link called VDL-4 and support navigation, communication and surveillance operations.

The EGNOS TRAN trials results led to the following conclusions:

• The ETRAN accuracy performance is comparable with “direct Egnos” performance and compatible with APV II requirements
• The availability of EGNOS corrections is strongly increased in high latitude where the GEO visibility is easily lost due to obstacles or low signal
• The conversion from SBAS to GBAS has been validated and proved to be a viable way to introduce EGNOS by reusing existing aviation equipment and standards. It could be a lower cost/backup solution for airport infrastructure.

The EGNOS-TRAN Aviation project started in July 2001 and was concluded in July 2003.