Boeing 737s serve markets previously filled by other midsize airliners.
The Boeing 707 is a mid-sized , long-range , narrow-body , four-engine jet airliner built by Boeing Commercial Airplanes from 1958 to 1979 . Boeing 737 . Many 737s serve markets previously filled by 707 , 727 , 757 , DC-9 , and MD-80 / MD-90 airliners , and the aircraft currently competes primarily with the Airbus A320 family .