Montréal–Mirabel International Airport (IATA: YMX, ICAO: CYMX), originally called Montréal International Airport, widely known as Mirabel and branded as YMX International Aerocity of Mirabel (YMX Aérocité internationale de Mirabel), is a cargo and former international passenger airport in Mirabel, Quebec, Canada, 39 km; (24 mi) northwest of Montreal. It opened on October 4, 1975, and the last commercial passenger flight took off on October 31, 2004.
Prior to the demolition of the terminal, Montréal–Mirabel International Airport was classified as an airport of entry by Nav Canada and was staffed by the Canada Border Services Agency (CBSA). A smaller AOE is still available at the Hélibellule FBO. It was one of two airports in Canada with sufficient right-of-way that can be expanded to accommodate 50 million passengers per year, the other being Toronto Pearson International Airport. A lack of traffic meant that Mirabel was never expanded beyond its first phase. It is one of only two non-capital airports with fewer than 200,000 passengers a year to be part of the National Airports System.
The airport was intended to replace the existing Dorval Airport as the eastern air gateway to Canada. Accordingly, from 1975 to 1997, all international flights to and from Montreal (except for flights to and from the United States) were required to use Mirabel. However, Mirabel's distant location, the lack of adequate transport links to urban centres and the continued operation of domestic flights from Dorval Airport made Mirabel very unpopular with travellers and airlines. It did not help that Montreal's economy declined relative to that of Toronto during the 1970s and 1980s. As a result, passenger levels never approached the levels that had been anticipated, and indeed remained lower than what Dorval could handle when renovated.
When the decision was made to consolidate Montreal's passenger traffic at one airport, Dorval was chosen, and Mirabel was relegated to the role of a cargo airport. Mirabel thus turned out to be a white elephant. Dorval Airport was renamed Montréal–Pierre Elliott Trudeau International Airport, after the Canadian Prime Minister whose government initiated the Mirabel project, the aim of which was to close and replace the Dorval airport. By surface area, it was the largest airport in the world that had ever been envisioned, with a planned area of 39,660 hectares (396.6 km2; 98,000 acres); King Fahd International Airport in Saudi Arabia, completed in 1999, eventually surpassed its surface area. In 1989, 32,780 hectares (81,000 acres) of the 39,660 hectares (98,000 acres) were deeded back to their original owners.
Today, Montréal–Mirabel International Airport is used almost exclusively for cargo flights, with passenger operations having ceased on October 31, 2004, 29 years after the airport's opening and many years of limited, primarily charter service. Bombardier Aerospace launches newly constructed units from its factory at Mirabel.