1. ENAV, 2012. Website http://www.enav.it.
2. EGNOS Aviation CBA for AFI;ESESA,2010
3. GNSS Sole Service Feasibility Study;Eurocontrol,2003
4. European GNSS Supervisory Authority, 2010. Website http://www.gsa.europa.eu.
5. Airworthiness Approval of Positioning and Navigation Systems, Advisory Circular 20–138B;FAA,2010