When ATC cannot clear you

When ATC cannot clear you (TC AIM RAC 1.6.1): traffic unknown, part of the aerodrome closed, or minima not met.

• "AT YOUR DISCRETION": surface hidden from the tower by an obstruction (not weather), or the non-manoeuvring area. Manoeuvre safely; ATC gives traffic info when possible.
• "UNABLE TO ISSUE CLEARANCE": controller has no authority to clear. Continuing anyway can bring TC regulatory action; ATC files an occurrence report.
• Field, water aerodrome or temporary landing area in the zone: also at your discretion; ATC gives traffic and obstruction info (TC AIM RAC 1.6.1.1(b)).
• Denial (operator closed the airport, or NAV CANADA directs no taxi clearance): ATC says no clearance can be issued, gives the reason and NOTAM, asks your intentions. If you go anyway and traffic permits, ATC passes safety info, notifies the operator and files an occurrence report (TC AIM RAC 1.6.1.1(d)).

Practice