Hi J
Apart from the obvious codes (74/5/6/7).
The UK codes are as follows, but don't know if they are International.
0023 SAR, 0030 Lost 0031 lost (working D&D). 2001-2077 a/c from non SSR environment.
4100 MAFF, 4307 Height Monitoring Unit (for RVSM checks).
7000 Conspicuity, 7001 L/L mil climeouts, 7003, Red Arrows, 7004 Aircraft performing aerobatics, 7010 Gliders, 7011 Microlights, 7012 Balloons, 7013 Gliders, 7016 Height Monitoring Unit, 7711-17 SAR, 7721-27 SAR, 7776 Ground Transponder test/trials.
Hope this is of interest
