Transponder – Canadian Flight Trainers

A transponder is an airborne electronic device that receives an interrogation signal from ground-based Secondary Surveillance Radar (SSR) and transmits a coded reply. The reply provides ATC with the aircraft’s identity (Mode A squawk code), altitude (Mode C), or both plus datalink (Mode S).

Transponder Operation

OFF: Transponder off — use only for maintenance or specific instructions
STBY (Standby): Warmed up but not transmitting replies — use while on the ground at busy airports until cleared to line up
ON (Mode A): Transmitting squawk code only — rarely used in Canada
ALT (Mode C): Transmitting code and altitude — standard operating mode in flight
IDENT: Press to briefly bloom the radar return for controller identification

Transponder Requirements

In Canadian controlled airspace above 12,500 ft and in Class C and B airspace, a Mode C transponder is mandatory. In RVSM airspace, a Mode S transponder is required. Always set the correct squawk code and confirm ALT mode before flight in controlled airspace.

Related Terms

See also: Transponder Codes, SSR, Squawk.