Rules of the Air Article 43

In the event that a controlled flight inadvertently deviates from its current flight plan, the following action shall be taken:1. Deviation from track: if the aircraft is off track, action shall be taken forthwith to adjust the heading of the aircraft to regain track as soon as practicable.2. Variation in true airspeed: if the average true airspeed at cruising level between reporting points varies or is expected to vary by plus or minus 5 percent of the true airspeed, from that given in the flight plan, the appropriate air traffic services unit shall be so informed.3. Change in estimated time: if the estimated time at the next applicable reporting point, flight information region boundary or destination aerodrome, whichever comes first, is found to be in error in excess of 3 minutes from that notified to air traffic services, or such other period of time as is prescribed by the appropriate ATS authority or on the basis of air navigation regional agreements, a revised estimated time shall be notified as soon as possible to the appropriate air traffic services unit.