There are ten airports in the Greater Toronto Area. Pearson, Waterloo, Billy Bishop and Hamilton have scheduled passenger service; however, the vast majority of passenger traffic goes through Toronto's Pearson International Airport, which is Canada's busiest airport and the country's major hub. Waterloo is a growing passenger service airport with a very active GA and training population. Billy Bishop is used for civil aviation, air ambulance traffic and regional scheduled airlines. Buttonville formerly had scheduled passenger service from Ottawa operated by Bearskin Airlines, but it has been discontinued. Hamilton acts as an alternative to Pearson and is popular with charters and discount airlines who want to avoid fees at Pearson, which is among the world's most expensive airports.