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Aircraft use transponders to communicate to ATC their position and status. Some squawk codes are reserved, such as 7700 (emergency), 7600 (communication failure), 7500 (hijacking), 1202 (glider), 1200 (VFR), etc. One of these, 7777, is apparently used for "military interception." What does this mean in the United States? Under what circumstances would it be used on a civilian / military aircraft?

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In countries outside of the US, 7777 may be used by test transponders (RABMs) to check correctness of radar stations (BITE). e.g. on top of a mountain.

In the US, it seems that it is used as well on active air defense missions without ATC clearance. This would mean that the interceptor aircraft would change it's squawk to 7777 for the military/civilian air traffic controller to see it properly (if not filtered out on civil radars).

A link to the US intercept procedures is here.

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    $\begingroup$ Why the downvotes? This is correct. $\endgroup$ – pericynthion Feb 9 at 22:58
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    $\begingroup$ Yep, I have been wrong for about 10 years now. I would have sworn the craft being intercepted was the squawker of 7777. Edited to add my link to the FAA doc. Deleted my wrong answer, and upvoted this. $\endgroup$ – Ryan Mortensen Feb 9 at 23:10
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    $\begingroup$ @RyanMortensen good thing you didn't get intercepted in the last 10 years :) $\endgroup$ – pericynthion Feb 10 at 2:19
  • $\begingroup$ @pericynthion yeah, I may need to have a chat with some people I have learned it wrong from and spread the knowledge. $\endgroup$ – Ryan Mortensen Feb 10 at 16:11
  • $\begingroup$ You know, now that I think about it, I bet I was told that by retired Air Force guys who mixed up the roles' codes. $\endgroup$ – Ryan Mortensen Feb 10 at 16:19
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According to the AIM 4-1-20(e):

  1. Under no circumstances should a pilot of a civil aircraft operate the transponder on Code 7777. This code is reserved for military interceptor operations.

The ATC orders don't add anything useful and a lot of security procedures are classified, or at least not publicly available on faa.gov. But it seems from that information that a) 7777 is important for interception operations, and b) civilian pilots must not use 7777. That implies that 7777 is reserved for interceptor aircraft, not the aircraft being intercepted.

The FAA's interception instructions for pilots say that intercepted aircraft should squawk 7700.

See this question too.

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