In sharp contrast to the A321, the values of the -900ER have continued to fall such that the variant is mainly worth less than the smaller -800.
In the spring of 2001, Boeing started studying the possibility of a -900X featuring more range and allowing more seats to be fitted. This necessitated the installation of additional exits aft of the wing. The -900X, renamed the -900ER, program has entered service in numbers, supplanting the existing -900.
The B737-900ER was therefore the largest B737 and the fourth member of the “New Generation”-family. Compared with the B737-800, the -900ER features a strengthened nose landing gear; a forward fuselage plug of 1,37m; an aft fuselage plug of 1,07m; a strengthened center fuselage body section; a revised tailskid; and a strengthened horizontal tail. Because of the extra exits, the maximum seating is increased to 215.
Boeing had to stem the orders being placed for the competitive A321-200 by developing the -900ER even if the issue of emergency exits prevented a similar capacity being achieved. The A321-200 had proved to be popular with a variety of carriers due to greater capacity and commonality with other members of the A320 family. In contrast to the -900, in a high density charter configuration the A321-200 can carry 230 or more passengers, only 10 less than the B757, also in a high density configuration and this is due to be increased further. The -900, though just under nine feet longer than the can still only carry a maximum of 189 passengers due to exit limits. The -900 was originally developed to meet the needs of scheduled carriers anxious to improve revenue earning potential from carrying more passengers in reasonable comfort. To overcome the limitations of the exits, Boeing added two additional emergency exits behind the wing. Both options add weight to the aircraft and thereby impact payload/range which has been compensated for by the addition of underfloor tanks. In many ways, the B737-900ER was viewed as a replacement for the B757 but such demand has instead been focused on the A321.
The A321-200 represents a more than credible competitor. Seating. The B737-900ER can carry a maximum of 215 versus the 220 of the A321 (since increased to 240 and higher). Cargo. The B737-900ER has a cargo capacity of 1,827ft3, approximately the same as 1,828ft3 of the A321 though the Airbus product does have the modified LD3 container capability. Cruise Altitude. The maximum altitude of the B737-900ER is 41,000 feet – after sufficient fuel has been burnt off compared with the 39,000 feet of the A321. This is a point that Boeing has sought to highlight citing the greater freedom to select routes. Some European customers in particular have also indicated that the higher cruise altitude has proved attractive. D Check. The B737-900ER D check interval is 23,800 hours, equating to 8 years based on eight hours per day compared with six and 12 years for the A321. Engines. With the same basic engine available on both aircraft types there should be little difference. CFM has the experience but fixed maintenance costs provided by IAE have proved attractive on the A321 which has by far the larger number of installed engines. Family Commonality. The B737-900ER has commonality with other members of the B737NG as well as cockpit commonality with the B737CG. The A320 family is extensive and MFF is possible through commonality with the A330/A340 family. Noise. Airbus show that the A321 is slightly noisier than the -900ER with the cumulative Chapter 3 margin also slightly worse.