McDonnell Douglas DC-10 jetliners operated by Northwest Airlines. In 1979, Northwest was flying DC-10 service on a round trip routing of Newark Liberty International Airport (EWR) - Detroit (DTW) - Chicago O'Hare International Airport (ORD) - Billings (BIL) - Great Falls (GTF) - Spokane (GEG) - Seattle (SEA). By 1982, the airline was operating the DC-10 on a round trip routing of Minneapolis/St. Paul (MSP) - Billings - Great Falls - Spokane - Seattle. The DC-10 was the largest aircraft ever to be operated in scheduled passenger service into the airport. For a short period in 1979, Northwest used a Boeing 747 to provide passenger service to MSP-BIL-SEA. This was at the tail end of a pilot/airline dispute. Northwest also served Billings with Boeing 727-200, McDonnell Douglas DC-9-30, McDonnell Douglas DC-9-50, McDonnell Douglas MD-80 and Airbus A319 jetliners over the years. In 1983, four airlines were operating mainline jet service into the airport: Continental Airlines with Douglas DC-9-10 and McDonnell Douglas DC-9-30 nonstop flights to Denver and Great Falls, the original Frontier Airlines (1950-1986) with Boeing 737-200 nonstop flights to Denver, Great Falls and Helena, Northwest Airlines with Boeing 727-200 nonstop flights to Great Falls, Helena, Minneapolis/St. Paul and Spokane with direct service to Chicago, Seattle and Portland, OR, and Western Airlines with Boeing 737-200 nonstop flights to Salt Lake City with direct service to Los Angeles and San Francisco. By 1985, Northwest had once again added nonstop service to Chicago O'Hare International Airport flown with Boeing 727-200 aircraft while United Airlines had begun flying Boeing 737-200 nonstop service to Denver. Also in 1985, the airport had commuter airline service operated by Big Sky Airlines, Centennial Airlines and Pioneer Airlines with the latter air carrier operating as Continental Express on behalf of Continental Airlines. Another airline which operated jet service into Billings was Horizon Air which in 1999 was operating Fokker F28 Fellowship twin jets with nonstop flights to Seattle on behalf of Alaska Airlines. By 2003, the airline was serving Billings with Canadair CRJ-700 regional jets. Horizon Air continues to serve the airport at the present time on behalf of Alaska Airlines with the Bombardier Dash 8 Q400 propjet which is the largest and fastest member of the de Havilland Canada DHC-8 regional turboprop family of aircraft. Additional airlines operating regional jets from the airport in the past included America West Express operated by Mesa Airlines with Canadair CRJ-200