When it was acquired by and merged into the original Frontier Airlines on October 1, 1967, Central was operating a fleet of Convair CV-600 turboprops as well as sixteen Douglas piston-powered DC-3s. Central was planning to introduce new Douglas DC-9-10 jets with the airline running a print ad in the Official Airline Guide announcing this upcoming DC-9 service; however, the DC-9s were never delivered due to the merger. Frontier continued to operate the Convair CV-600s for a time but then retired them in favor of Convair CV-580 turboprops which were the backbone of Frontier's fleet in the late 1960s. Frontier would eventually introduce Boeing 737-200 jet service to smaller cities previously served by Central including Fort Smith, AR; Joplin, MO; Lawton, OK; Manhattan, KS; Pueblo, CO; Salina, KS; and Topeka, KS. In 1986 Frontier Airlines (1950-1986) was merged into Continental Airlines. In 2010 Continental was merged into United Airlines.