Terminal radar service area
In United States aviation, a terminal radar service area (TRSA) is a delimited airspace where radar and air traffic control services are made available to pilots flying under instrument flight rules or (optionally) visual flight rules, to maintain aircraft separation. TRSAs most often surround busy U.S. airports. In recent years, many of them have been replaced by Class C or Class B airspace. Terminal Radar Service Area was established as part of a program to create terminal radar stations at selected airports. Because they were not subject to the rulemaking process of 14 CFR Part 91, they do not fit into any existing U.S. classifications of airspace, and have been classified as non-part 71 airspaces.