There has never been a curfew at Montréal-Trudeau. Like all major airports and other types of airport infrastructures, Montréal-Trudeau airport is open 24 hours a day. However, there are certain restrictions on night flights, specifically on flights by wide-body jets weighing more than 45,000 kg (e.g., Airbus A320, Boeing 737).
Takeoffs: Midnight to 7 a.m.
Landings: 1 a.m. to 7 a.m.
Aéroports de Montréal (ADM) does, however, have the right and the authority to make exceptions for medical emergencies, delays beyond the carrier’s control and adverse weather conditions. A strict internal policy applies in such cases. In particular, there are only a small number of exemptions for regular flights (four departures per day on average), and they must be supported by sound operational reasons. The exemptions are also contingent upon adherence to the noise abatement measures in force.
Note also that especially noisy aircraft cannot be granted exemptions for night flights; these include the Antonov, B727, B737 100 and 200 series, B747, DC9, DC10, Ilyushin, L101, MD 80 and MD-11.