By the early 1990s , it became clear that the new Airbus A320 was a serious threat to Boeing 's market share . Airbus won previously loyal 737 customers such as Lufthansa and United Airlines . By the early 1990s , it became clear that the new Airbus A320 was a serious threat to Boeing 's market share , as Airbus won previously loyal 737 customers such as Lufthansa and United Airlines .