High Quality Content by WIKIPEDIA articles! Frontier Airlines was formed from a merger of Arizona Airways, Challenger Airlines, and Monarch Airlines on June 1, 1950. They established their headquarters at Stapleton Airport in Denver. However, the airline dated itself to November 27, 1946, when Monarch Airlines began service in Colorado, Utah, New Mexico, and Arizona. Frontier Airlines served cities in the Rocky Mountains bounded by Salt Lake City to the west, Billings to the north, Denver to the east, and Phoenix to the south. The new airline served 40 cities in the Rocky Mountain region with 12 DC-3s and 400 employees.