AIM Text
- If an aircraft with a coded radar beacon transponder experiences a loss of two‐way radio capability, the pilot should adjust the transponder to reply on Mode A/3, Code 7600.
- The pilot should understand that the aircraft may not be in an area of radar coverage.
Source: FAA Aeronautical Information Manual · current edition · paragraph 6-4-2.
Research Notes
AIM 6-4-2 covers Transponder Operation During Two-Way Radio Communications Failure — proper squawk code use during comm failure.
The 7600 protocol: Squawk 7600 immediately upon recognizing comm failure. ATC will see the code and:
- Attempt contact on 121.5
- Attempt contact via the previous frequency
- Use light gun at towered airports for arriving aircraft
- Provide separation services and route adjustments
If comms restore: Stop squawking 7600, contact ATC, and continue per clearance. ATC may ask if you've made any deviations during the comm failure.