In December 1985, Boeing
decided to offer a 737 twinjet with a 10-foot (3 m) fuselage stretch that
would add three more economy seat rows and two more first class seats, or
21 more two-class passengers when compared with earlier the 737-300.
Boeing engineers had been studying a
larger 737 for a number of years -- one with a fuselage lengthened enough
to bring capacity to 147 seats in mixed-class service. Airlines operating
the 737-300 model had been pleased with its low fuel consumption and high
dispatch reliability, and they urged the development of an airplane with
slightly more capacity, but one that would blend easily into existing
fleets of 737s.
Airlines especially liked the fact
that the 737-400 is a straightforward derivative of the 737-300;
therefore, 737-300 pilots could be cross-qualified. Flight crews who can
operate both a 737-300 and -400 give airlines great flexibility in
scheduling and subsequent savings in fleet operations.
The 737-400 was formally launched in
June 1986 to augment the fleets of carriers needing more capacity to meet
traffic growth. Rollout of the first 737-400 was Jan. 26, 1988. Following
an 8-month flight-test program, first delivery was Sept. 15, 1988, to
kick-off customer Piedmont Airlines.
The 737-400 twinjet retains basic
systems commonality with the -300. Thus, it is a short- to medium-range
airliner with increased passenger seating, low noise levels, low fuel
consumption and high dispatch reliability.
Apart from the longer fuselage,
other changes from the 737-300 are engines of slightly higher thrust,
strengthened wing components and landing gear, and an environmental
control system (the airplane's "air conditioning") that is
enlarged to handle higher passenger loads. The airplane is 119 feet 7
inches (36.4 m) long with a tail height of 36 feet 6 inches (11.1 m) and
wingspan of 94 feet 9 inches (28.9 m).
The engines that power the 737-400
are the CFM56-3, built by CFM International, a company owned by General
Electric of the United States and Snecma of France. The engine is a
high-bypass-ratio powerplants rated at 22,000 pounds thrust and offers a 19
percent fuel burn improvement over engines powering early models of the
737 and 727. The quietness of takeoffs is surprising: generally the
takeoff noise cannot be heard outside of the airport boundaries. Much of
the noise reduction and low fuel consumption of the 737-400 is because of
this superior engine.
Other advances in the 737-400
stemmed from basic design.
During development work on the
airplane, Boeing kept as a goal long service life and low maintenance, as
well as elimination of any excess weight in the airplane. The latest
aluminium alloys are used in the structure, along with increased carbon
composite parts. A special program of corrosion prevention is designed to
assure customers that the airplane will maintain its original structural
soundness in any operating environment.
Some operators fit additional seats
into the 737-400. The basic U.S. configuration is 147 seats (137 economy
with 31-inch pitch between seats and 10 first class at 36-inch pitch).
Other options include 159 all-economy seats at 32-inch pitch, and an
inclusive-tour layout of 168 passengers at 30-inch pitch.
No matter which seating arrangement
is chosen, passengers benefit from the 737-400's roomy interior with large
overhead stowage bins for carry-on baggage and a 20-inch (500-mm) center
aisle with six-abreast seating.
With the longer fuselage, airlines
gain larger cargo areas. With a total usable cargo volume of 1,373 cubic
feet (38.9 m3), the 737-400 still offers a freight hold
accessible from the ground without ladders.
The basic airplane gross weight is
138,500 pounds (62,820 kg), with an optional high-gross-weight version of
150,000 pounds (68,040 kg). Fuel capacity is 5,311 gallons (20,105 L),
expanding to 6,295 gallons (23,825 L) with two optional tanks.
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