1. Joint Planning and Development Office 2004, Next Generation Air Transportation System Integrated Plan. http://www.jpdo.aero
2. Swenson,H, Barhydt, R. and Landis M. (2006) Next Generation Air Transportation System (NGATS) Air Traffic Management (ATM)-Airspace Project Reference Material External Release Version, (NASA 2006) http://www.aerospace.nasa.gov/nra_pdf/airspace_project_c1.pdf
3. NASA, 1999, Concept Definition for Distributed Air/Ground Traffic Management (DAG-TM), http://www.asc.nasa.gov/aatt/dagconop.pdf