Boeing 737s avoids markets presently filled by MD-80/MD-90 airliners.
Boeing 737 . The 737 is Boeing 's only narrow-body airliner in production , with the 737 Next Generation ( -700 , -800 , and -900 ER ) variants currently being built . 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 .