Ozark Air Lines arrived in 1955; its DC-3s flew Chicago Midway Airport - Dubuque - Waterloo - Mason City - Fort Dodge - Sioux City. By 1960 Ozark was flying Fairchild F-27s to Waterloo. Ozark Douglas DC-9-10s arrived in 1966. (Runway 12/30 had been extended from 5400 to 6500 feet around that time). In 1967 Ozark DC-9s flew nonstop to Chicago O'Hare Airport and direct to Denver via Sioux City; other flights were Fairchild F-27s, Fairchild Hiller FH-227s and Martin 4-0-4s. The April 1970 Ozark timetable lists nonstop DC-9s to Washington D.C. Dulles Airport continuing to New York LaGuardia Airport (LGA); by 1971 Ozark's direct DC-9 to Washington and New York stopped in Peoria. Besides DC-9-10s, Ozark also served Waterloo during the 1970s with McDonnell Douglas DC-9-30s and Fairchild Hiller FH-227s. In the 1975 Official Airline Guide Ozark was the only airline at Waterloo, with nonstops from Cedar Rapids, Chicago O'Hare International Airport, Des Moines, Dubuque, Mason City, Moline, Omaha, Rochester, MN, and Sioux City, a total of eighteen weekday flights, nine DC-9s and nine FH-227s. In 1976 Ozark was operating nonstop as well as direct, one stop DC-9s to Denver and one-stop DC-9s to Minneapolis/St. Paul; and direct and nonstop to Chicago O'Hare with up to seven flights a day in addition to direct flights to Omaha, St. Louis and other cities. By 1982 Ozark flights at Waterloo were all DC-9s, including direct flights to Fort Lauderdale, Fort Myers and Miami in Florida via St. Louis. Ozark successor Trans World Airlines flew DC-9s to its St. Louis hub; TWA ended mainline Waterloo service by early 1988, replaced with Trans World Express.