The Boeing 737 series has been one of the most successful commercial aircraft of all time. The first generation, comprising the Original and Classic variants, were in production until 2000, and the Next-Generation 737s were in production from the late 1990s until 2019. It is the 26th anniversary of the first 737 Next-Generation flight, which is a good opportunity to examine the modifications Boeing made to the aircraft from the Classic era.

Boeing 737 Original and Classic series

Photo: Jake Hardiman | Simple Flying

Announced by Boeing in the mid-1960s, the first Boeing 737 was unveiled in 1967 and was nicknamed 'Baby Boeing' as it was smaller than the previous civilian aircraft designed by the company. The 737-100 had six-abreast seating, and the engines were mounted under the wing. By 1987, two variants were available - the -100 and the -200, and they were the most successful commercial aircraft in history then.

The Classic series began with the 737-300. This had higher capacity and improved fuel efficiency than the Original series. New engines were added that increased thrust, increased wingspan to improve aerodynamics and a redesigned tailfin. The 737-400 was larger again, and the 737-500 was the same size as the Original series but was updated with an improved design.

By 1991, over 3,000 orders had been placed across five variants. At the time of writing, data from ch-aviation.com shows that there are still 512 active Boeing 737 Classic aircraft.

Boeing 737 Next-Generation

The Next-Generation series was launched in the 1990s and were designed to improve upon the Classic series without designing an entirely new aircraft. Boeing needed it to be faster, more efficient and have a longer range to compete with rivals.

The wing was redesigned, resulting in a larger surface area with a higher span and modified flaps. The design changes produced a lighter wing than the original design, providing improved aerodynamics and helping to improve fuel efficiency. The range of the NG increased by over 400NM, and they could fly at a higher altitude of FL410 and a faster cruise speed than the Classic series.

Navigation systems were enhanced, with GPS introduced and an improved glass cockpit with six information and flight display screens. Improved terrain and wind shear warning systems can be fitted in addition to enhanced display and flight information systems for pilots.

Photo: Vincenzo Pace | Simple Flying

Boeing developed a winglet that became available from the -800 series in the early 2000s and could be retrofitted to earlier models. The winglets extended the range again, reduced fuel consumption further and enabled an increase in payload.

Boeing also increased the manufacturing process's efficiency to speed up aircraft production. Fewer parts comprise the NG and are easier to maintain than the Classics.

The NG series eventually had five variants - the -600, -700, -800 and -900. These were introduced in phases between 1993 and 2005, with the -800 series being best selling of these. The 737-800 has a capacity for up to 189 passengers, but the largest is the 737-900ER, with capacity of up to 220 passengers.

Other technical improvements, some of which could be retrofitted, included upgraded CFM56-7 engines with improved fuel efficiency and reduced noise, new landing gear, new carbon brakes and even an option for short-field performance functions. Airstairs became available, making it a more versatile aircraft and is something that Ryanair, in particular, exploits to minimize turnaround times. Upgrades and enhancements were also made to the interior.

The Boeing 737 has been through several iterations, and as we are now firmly in the next phase with the 737 MAX family, it will continue to be a workhorse of the industry for many years.

What is your favorite version of the aircraft? Please tell us in the comments below.