What does AIM say about transponder code 7777 and civil aircraft?

1. 1A civil pilot must never use it
2. 2A civil pilot uses it after a radio failure, to alert ATC
3. 3A civil pilot uses it when flying in a formation flight
4. 4A civil pilot uses it only below 10,000 feet MSL in daylight

Source: Aeronautical Information Manual (FAA, Basic with Change 3, 9 July 2026), AIM 4-1-20 Transponder and ADS-B Out Operation — Code Changes, page 223