Definition
National Security Areas are sections of airspace, defined by vertical and lateral limits, established at locations where there is a need for increased security and safety of ground facilities. Pilots are requested to voluntarily avoid flying through NSAs. When circumstances require a more stringent measure, flight in an NSA may be temporarily prohibited by regulation under 14 CFR Part 99, with the prohibition publicized through a Notice to Air Missions (NOTAM).
Plain English
An NSA is a piece of airspace around a sensitive ground site where the FAA asks pilots to please stay out for security reasons. Most of the time it's a request, not a rule — but the FAA can make it a hard rule when the situation calls for it, and they'll announce that change through a NOTAM.
Context Anchor
Seen in special use airspace discussions, preflight planning, chart review, and notices about sensitive ground facilities.
Why Pilots Care
Entering an NSA without authorization can trigger military interception or enforcement actions that interrupt the flight.
Intuition Check
Do not assume a National Security Area is automatically a no-fly zone. Usually it is an area pilots are asked to avoid; it becomes off-limits only when an active rule or official notice prohibits flight there.
Example Sentence 1
On the way to her destination, she noticed an NSA depicted on the sectional chart and altered her route slightly to avoid overflying it.
Example Sentence 2
While flying VFR, the instructor pointed out the NSA boundaries to the student and explained the avoidance request.