| Mode 3/A meaning | Squawk |
| Autonomous ops within TRAs | |
| SAR Ops | |
| NATO Air Defence Priority (first in series) | |
| Pipeline / powerline inspection | |
| MPA / FPA / METMAN conspicuity | |
| Red Arrows transit / display | |
| General conspicuity | |
| Paradropping | |
| Danger areas general | |
| High-energy manoeuvres | |
| | Mode 3/A meaning | Squawk |
| SSR unreliable | |
| Non-SSR environment | |
| Special purpose code - hi-jacking | |
| RN Ships | |
| Radio failure | |
| General emergency | |
| Open Skies observation | |
| Military low level conspicuity / climb-out | |
| Royal flights - helicopters | |
| FIR lost | |
|