Squawk code · special
Squawk 4000: Military operations area
Squawk 4000 is the US code for military aircraft operating in restricted or warning areas or on VFR military training routes.
Squawk 4000 is used by US military aircraft working in restricted or warning areas, or on low-level VFR military training routes. It tells controllers the aircraft is doing military training in airspace set aside for it.
What 4000 means
The FAA's AIM (4-1-20) says military pilots operating VFR or IFR within restricted or warning areas should set code 4000 unless ATC assigns another. The same applies on VR (VFR military training) routes, which are low-level corridors where military jets practise high-speed, low-altitude flying. Restricted and warning areas are blocks of airspace where hazardous activity such as live firing, air combat training or high-speed manoeuvring takes place.
Where you see 4000
- Over military ranges in Nevada, Utah, California, Arizona and New Mexico.
- Off the Atlantic, Gulf and Pacific coasts in warning areas, where Navy and Air Force jets train over water.
- Along VR routes, often crossing rural areas at a few hundred feet.
How 4000 appears on heywhatsflying
Military aircraft squawking 4000 are among those we flag on military and government now, when they broadcast position at all. Many fighters train with ADS-B Out turned off, so you may see a 4000 code with no position (Mode S only) or not at all. Our guide why military aircraft show or don't explains the rules.
Low-level routes and what they mean for others
Military training routes are published on aeronautical charts as IR (instrument) and VR (visual) routes, and general aviation pilots are encouraged to check whether a route is active before crossing it. Jets on these routes can fly at 250 knots or faster below 10,000 ft, which is above the normal US speed limit for that altitude, under a specific exemption for military training. A 4000 code on a radar scope gives controllers a quick way to see that a target is on such a route or in such an area, rather than a civil aircraft that has strayed.
Related codes: 7777 (military interceptors) and 0000. See the full squawk code index.
Questions
What does squawk 4000 mean?
It is the US code for military aircraft operating in restricted or warning areas, or on VFR military training routes, when ATC has not assigned another code.
Why do I see 4000 without a position?
Many military aircraft keep their transponder on for ATC but do not broadcast ADS-B position. Some trackers then show the code but cannot place the aircraft without multilateration.