Boeing 737-400 vs. Boeing 737-600

The Boeing 737-400, part of the 737 Classic series, is a narrow-body, twin-engine airliner developed to meet the evolving requirements of the short to medium-haul market. First introduced in 1988, the 737-400 expanded upon the success of its predecessor, the 737-300. The -400 variant entered manufacturing shortly after finalization of design plans between Boeing and launch customer Piedmont Airlines (later merged into US Airways). It gives increased capacity and range, offering an option in between Boeing's 737-300 and the 757-200.

The fuselage incorporated a key 8 foot expansion to enable typical accommodation for up to 170 passengers in a 2-class layout. Other changes included increased weights and structural reinforcements, enhanced avionics/flight controls, and higher thrust CFM powerplants required for the heavier max takeoff figures. Cost efficiencies were achieved keeping cockpit continuity with the ubiquitous 737 flight deck suite.

Spanning 119.6 feet (36.5 meters) in length with a wingspan of 94.5 feet (28.8 meters), the 737-400 was designed to accommodate the growing demand for larger single-aisle aircraft. The aircraft typically seats 144 passengers, providing more space and comfort compared to earlier models in the series. This increased capacity made the 737-400 an attractive option for airlines seeking to transport more passengers on popular routes, without the need for a larger, wide-body aircraft. Equipped with two CFM International CFM56-3C1 engines, the 737-400 delivers a total thrust of 44,000 lbf (196.0 kN). This engine configuration, combined with a fuel capacity of 5,310 US gallons (20,100 liters), allows the aircraft to achieve a range of 2,079 nautical miles (3,850 kilometers).

In the competitive commercial aviation market of its time, the Boeing 737-400 contended with models like the McDonnell Douglas MD-80 series. Its introduction marked another milestone for Boeing in the evolution of the 737 family, solidifying the company's position in the market for short to medium-haul airliners. Airlines such as Alaska Airlines, Turkish Airlines, and British Airways incorporated the Boeing 737-400 into their fleets. The aircraft's operational role was significant, enabling these carriers to expand their route networks and increase flight frequencies, particularly in domestic and regional markets.

Launched in 1998, the Boeing 737-600 is the smallest aircraft in the 737 Next Generation (NG) series. It succeeded the 737-500, and was a significant evolution in Boeing's narrow-body offerings. It featured many upgraded features from the previous 737s, including aerodynamics, engines, and avionics. As the smallest NG variant, the 737-600 was designed for efficiency and adaptability, catering to airlines requiring a compact jet for short to medium-haul routes.

This aircraft extends 102.4 feet (31.2 meters) in length with a wingspan of 112.6 feet (34.3 meters). The 737-600, with a typical seating capacity for 123 passengers, offers an ideal balance between passenger comfort and efficiency, making it a fitting choice for airlines serving routes with moderate passenger demand. Equipped with two CFM International CFM56-7B20 engines, the 737-600 has a total thrust of 45,400 lbf (202.0 kN). This engine power, coupled with a fuel capacity of 6,868 US gallons (26,000 liters), gives the -600 a range of 3,051 nautical miles (5,650 kilometers). The 737-600 has a cruise speed of 528 mph (850 km/h) enabling airlines to maintain efficient and swift operations, particularly beneficial for regional network connections.

In the late 1990s and early 2000s, the Boeing 737-600 competed with aircraft such as the Airbus A318 and Bombardier CRJ series, offering airlines a modern alternative in the narrow-body market. Airlines including Scandinavian Airlines (SAS), Westjet, and Air Algerie operated the Boeing 737-600. Ultimately, the -600 variant was not a popular model of the 737 due to its economics. The -700, only slightly heavier, had a much greater payload. Additionally, the larger market was moving more towards higher capacity narrow-bodies with lower unit costs and greater revenue opportunities.