Special flight rules area
In United States aviation, a special flight rules area (SFRA) is a region in which the normal regulations of flight do not apply in whole or in part, especially regulations concerning airspace classification, altitude, course, and speed restrictions, and the like. == Washington, DC Special Flight Rules Area == Following the terrorist attacks of September 11, 2001, the airspace around Washington DC underwent a number of changes designed to restrict flying around the city.
Source: Wikipedia — Special flight rules area (CC BY-SA 4.0)