In the United States, a few types of SUAs exist: •
Military Training Routes (MTR) are aerial corridors in which military aircraft can operate below 10,000 feet faster than the maximum safe speed of 250 knots that all other aircraft are restricted to while operating below 10,000 feet. The routes are the result of a joint venture between the
Federal Aviation Administration and the
Department of Defense to provide for high-speed, low-altitude military activities. •
Controlled Firing Areas (CFA) contain activities that may be hazardous to nonparticipating aircraft, but ceased immediately when spotter aircraft, radar, or ground lookout positions indicate an aircraft might be approaching the area. They are not depicted on charts. •
National Security Areas (NSA) are sections of airspace through which flight is discouraged for reasons of national security. Aircraft are strongly advised to remain clear, or to request permission from the appropriate agency, though this is not necessary. •
Alert Areas are sections of airspace where a high volume pilot training or otherwise unusual aerial activity is taking place. They're used to advise pilots when to be particularly alert. ==References==