Boeing 737-900 United AirlinesBoeing 737 900 United Airlines airplane model. United Airlines 737 900 Max 9 airplane model. Until its launch on September 5, 1994 the 737 800 was known as the 737 400X Stretch. Compared with the 400, the 800 is 3. 02m (9ft 9in) longer, taking typical two class seating from 146 to 162, while range is significantly increased. The 800 has sold strongly since its launch, and early 2002 was the highest selling Next Generation model. First flight was on