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