1. http://www.nats.co.uk/
2. ICAO 2004 Manual on Volcanic Ash, Radioactive Material and Toxic Chemical Clouds International Civil Aviation Organization Doc. 9691
3. WMO/ICAO 2010 5th International Workshop on Volcanic Ash: Report http://www2.icao.int/en/anb/met-aim/met/iavwopsg/Meeting%20Documents/IAVWOPSG%20Workshop%20No.%205/Workshop%20No.%205%20Report.pdf
4. Guffanti , M. Miller , E. K. 2002 Reducing the threat to aviation from airborne volcanic ash http://volcanoes.usgs.gov/ash/trans/aviation_threat.html