When United Airlines, a long-time Boeing customer, purchased the Airbus A320, the former company responded by launching the 737 Next Generation program, or 737NG, to compete against Airbus's advanced fly-by-wire technology.

(© myself)

Stretched to 138 ft 2 in, the 737-900 is the longest variant of the 737NG. It filled the niche left behind by the discontinued Boeing 757-200 and competes with the Airbus A321. Alaska Airlines launched this variant in 1997 and took delivery on May 15, 2001. The 737-900 retains the maximum takeoff weight and fuel capacity of the 737-800. The capacity of the aircraft ranges from 189 in a high-density economy layout or approximately 177 in a two-class layout. Variants of the 737-900 include the -900ER and the -900 BBJ3.

Many thanks to @MrZa for allowing me to modify his amazing P8-A Poseidon for the making of this aircraft!