- 4096 Mode C transponder means they are 4,096 combination of numbers from 0000 through 7777 and mode C means that it has altitude encoding
- OFF: no transmission aircraft is as “primary”
- STBY: no transmission but unit is powered
- ON: Mode A operation; squawk code only is transmitted
- ALT: Mode C operation: pressure altitude is transmitted
- IDENT: will shine the aircraft for controller to find
- VFR code: 1200
- Hijacking code: 7500
- Communication failure code: 7600
- Emergency code: 7700
- FAR 91.215 & AIM 4-1-20 unless Class G it must be turned on and reporting altitude
- Transponder required in A, B and C airspaces
- Within 30 miles of class B airspace (mode C veil line)
- All flights above 10,000 feet MSL
