Calgary-based WestJet Airlines said Tuesday it has taken a major step toward reaching a code-sharing deal with Cathay Pacific.

It has signed an interline agreement with the Hong-Kong-based airline, allowing passengers on Cathay flights to travel on one itinerary through the gateways of Vancouver and Toronto, continuing via WestJet to Calgary, Edmonton, Winnipeg, Ottawa, Montreal or Halifax.

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The interline agreement will allow Westjet to carry Cathay Pacific passengers from Toronto and Vancouver to other Canadian cities.

"This interline agreement signifies the progression of WestJet's strategic plans to expand our business into international markets and offer guests the opportunity to travel seamlessly from points in the Cathay Pacific network to cities in our Canadian network," said WestJet executive vice-president Hugh Dunleavy.

Under interline agreements, airlines collaborate on tasks like baggage handling. Interline pacts often pave the way for code-share agreements, in which one airline can sell a seat on another carrier's plane.

For years, the two airlines have discussed a code-share agreement, which allow each airline to put its flight code on a single flight operated by one of the partners.

WestJet initially had problems with its reservation system, which prevented it from integrating flights with Cathay, but that system was upgraded last fall.

Such agreements are key to WestJet, which has only one type of plane in its fleet -- the Boeing 737. Since those 136-seat aircraft aren't suited for long-haul flights, WestJet needs to find other ways of bringing international traffic into its network.

With files from The Canadian Press