Boeing 737s avoids markets presently filled by DC-9 airliners.
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 .
Boeing 737s
avoids
markets presently filled by DC-9 airliners
serve