Airlines began separating full-fare and discounted economy-class passengers in the late 1970s. In 1976, KLM introduced a Full Fare Facilities (FFF) service for its full fare economy-class passengers, which allowed them to sit at the front of the economy cabin immediately behind first class, and this concept was quickly copied by several other airlines including Air Canada.[5] Both United Airlines and Trans World Airlines experimented with a similar three-class concept in 1978, but abandoned it due to negative reactions from discount economy-class travelers who felt that amenities were being taken away from them.[6] United also cited the difficulty of tracking which passengers should be seated in which section of the economy cabin on connecting flights.[7] American Airlines also began separating full-fare economy passengers from discounted economy passengers in 1978, and offered open middle seats for full-fare passengers.[8]