1. Secretan E. (2011). Standard vs. Enhanced Digital Products. Proceedings of Digital Chart Agent Industry Meeting 13 December 2011. Maryland, USA.
2. RTCA. (2012). http://www.rtca.org/. Accessed 9 June 2012.
3. SESAR [Single European Sky Air Traffic Management Research Program]. (2012). http://www.eurocontrol.int/content/sesar-and-research. Accessed 14 January 2012.