What's an NSA?

You've seen national security areas (NSAs) on your charts for years, but you probably didn't know what they were called. The bold, segmented magenta lines enclose an area with the legend, "Notice — for reasons of national security, pilots are requested to avoid flight below 7,700' msl in this area." (The altitude varies depending upon the area, of course.)

An NSA is "airspace of defined vertical and lateral dimensions established at locations where there is a requirement for increased security of ground facilities," according to the Aeronautical Information Manual. "Pilots are requested to voluntarily avoid flying through an NSA. When it is necessary to provide a greater level of security, flight through an NSA may be temporarily prohibited pursuant to the provisions of 14 CFR 99.7, Special Security Instructions."

When there is a security reason for restricting flight operations within an NSA, the FAA will issue a notam.

"An NSA is preferable to a restricted or prohibited area because it is flexible," said Heidi Williams, AOPA manager of air traffic. "Once a prohibited area is established, it rarely goes away, and pilots lose another chunk of navigable airspace."

Source:  AOPA