ATC clearances vs instructions

An ATC clearance is an authorization to proceed under stated conditions: cleared to enter a zone, cleared for takeoff, cleared to land. An ATC instruction is a directive to do or not do something now: turn left, hold short, maintain 3,500. You can spot a clearance by some form of the word "clear" in it (TC AIM RAC 1.6).

• A clearance you accept and comply with. If you cannot comply, tell ATC at once, the clearance may then be changed or cancelled (TC AIM RAC 1.6).
• An instruction you must comply with and acknowledge, as long as safety is not jeopardized (CAR 602.31).
• Read back a clearance so ATC can confirm you got it right: always for IFR, and for VFR when ATC asks (CAR 602.31).
• A clearance or instruction is only valid in controlled airspace (TC AIM RAC 1.6).

Trap: a clearance is permission you accept, an instruction is an order; you acknowledge both, but you are never forced to fly an unsafe clearance, ask for an amended one.

Practice