range in restrictiveness, from areas where flight is always prohibited except to authorized aircraft, to areas that are not charted but are used by military for potentially hazardous operations (in this case, the onus is on the military personnel to avoid conflict). Refer to the external links for more specific details. References External links Airspace in the U.S., from the FAA's Aeronautical Information Manual UK Manual of Air Traffic Services, Part 1 US Airspace Aeronautical Charts Air traffic control Classification systems by subject de:Luftraum#Luftraumstruktur