Written with AI assistance and may contain mistakes. Verify against the official Transport Canada publications before relying on anything here.

Radio communication failure

Radio failure: lose two-way ATC contact. The rule depends on flight rules.

	IFR (CAR 602.137)	VFR (CAR 602.138)
Applies	IFR in, or cleared into, controlled airspace	VFR
Goal	Stay findable, stay on expected route, do not leave the airspace	Stay VFR, leave Class B, C, or D
Action	Stay on frequency, stay findable, climb if vector left low	Leave the airspace

Trap: applying the VFR "leave the airspace" rule to IFR failure, or reverse. Entering cloud to "press on" to destination.

IFR failure

Maintain listening watch on appropriate frequency, for control messages or further clearance.
Acknowledge any message by any means available.
Attempt to contact any ATS facility or another aircraft: report failure, ask them to relay to last ATC unit contacted.
Still no communications (direct or by relay): follow Canada Air Pilot (CAP) and Canada Flight Supplement (CFS) procedures, unless ATC already gave specific instructions for an anticipated failure.
Failure while vectored below minimum IFR altitude on the approach chart (TC AIM RAC 1.5.5): climb immediately to appropriate published minimum altitude, unless able to continue in VMC.

Situation	Action	Cite
In Class B, C, or D, control zone	Land at the aerodrome for which the zone is established	CAR 602.138
In Class B, C, or D, otherwise	Leave by the shortest route	CAR 602.138
In Class E or G, not intending to enter B, C, or D	May follow the leave-the-airspace procedure	TC AIM RAC 4.4.8
Failure outside B/C/D, blocks clearance or contact, no suitable aerodrome nearby	May enter B/C/D under VFR and carry out leave-the-airspace steps	TC AIM RAC 4.4.8
Suitable aerodrome nearby	NORDO arrival procedure recommended	TC AIM RAC 4.4.5

Then:

Inform ATC as soon as possible: phone (cell or satellite) once steps above are done. Numbers in CFS (TC AIM COM 1.7).
Controlled aerodrome: watch tower for light-gun signals, follow them.