JO 7110.65 5-2-1

General. Mode 3/A is designated as the common military/civil mode for air traffic control use.

Make beacon code assignments to only ADS-B and/or transponder-equipped aircraft. NOTE-

Aircraft equipped with ADS-B are also still required to have an operable transponder. The ATC-assigned beacon code is one of the required message elements of ADS-B Out.

Unless otherwise specified in this section, a facility directive, or a letter of agreement, issue beacon codes assigned by the computer. Computer-assigned codes may be modified as required. NOTE-

The computer will assign only discrete beacon codes unless all the discrete codes allocated to a facility are in use.

TERMINAL. Aircraft that will remain within the terminal facility's delegated airspace must be assigned a code from the code subset allocated to the terminal facility.

TERMINAL. Unless otherwise specified in a facility directive or a letter of agreement, aircraft that will enter an adjacent facility's delegated airspace must be assigned a beacon code assigned by the ARTCC computer. NOTE-

This will provide the adjacent facility advance information on the aircraft and will cause auto-acquisition of the aircraft prior to handoff. When an airborne aircraft that has been assigned a beacon code by the ARTCC computer and whose flight plan will terminate in another facility's area cancels ATC service, appropriate action should be taken to remove flight plan information on that aircraft.

PHRASEOLOGY-

SQUAWK THREE/ALFA (code),

or

SQUAWK (code).

REFERENCE-

FAA Order JO 7110.65, Para 5-3-3 , Beacon/ADS-B Identification Methods.

FAA Order JO 7110.65, Para 5-3-4 , Terminal Automation Systems Identification Methods.

Code 4000 should be assigned when aircraft are operating on a flight plan specifying frequent or rapid changes in assigned altitude in more than one stratum or other category of flight not compatible with a discrete code assignment. NOTE-

Categories of flight that can be assigned Code 4000 include certain flight test aircraft, MTR missions, aerial refueling operation requiring descent involving more than one stratum, ALTRVs where continuous monitoring of ATC frequencies is not required and frequent altitude changes are approved, and other flights requiring special handling by ATC.

Military aircraft operating in restricted/warning areas or on VR routes will squawk 4000 unless another code has been assigned or coordinated with ATC.