Boeing 737-300

The 737-300 was the first major revision of the 737 and the first model of the series later known as the 737 Classic. Development began in 1979: Boeing wanted more capacity and range and an aircraft upgraded to modern specifications while keeping commonality with earlier variants. Preliminary specifications were released at the 1980 Farnborough Airshow, and in March 1981 USAir and Southwest Airlines each ordered 10 aircraft, with an option for 20 more. It competed with the MD-80, later the MD-90, and soon the Airbus A320 family.

The key change was the engine. A team led by Boeing engineer Mark Gregoire worked with CFM International to select, modify and install the CFM56-3B-1 high-bypass turbofan, which brought significant gains in fuel economy and a large reduction in noise but posed a problem: the 737 sat low to the ground and the new engine was larger in diameter than the original Pratt & Whitney units. The answer was to reduce the size of the fan, place the engine ahead of the wing and move the accessory gearbox from the bottom of the engine to the side, which gave the nacelle its distinctive flat-bottomed intake nicknamed the “hamster pouch”. The lower bypass ratio reduced thrust from 24,000 to 20,000 lbf (107 to 89 kN).

The fuselage was extended around the wing by 9 feet 5 inches (2.87 m), raising capacity to 149 passengers. The wing was refined: the wingtip was extended 9 inches (23 cm) and the span by 1 foot 9 inches (53 cm), and the leading-edge slats and trailing-edge flaps were adjusted. The tailfin was redesigned, the flight deck could be fitted with an optional EFIS electronic flight instrument system, and the passenger cabin received improvements similar to those developed for the Boeing 757.

The prototype, the 1,001st 737 built, rolled out of the Renton plant on January 17, 1984, and first flew on February 24, 1984, with Jim McRoberts at the controls. Together with two production aircraft it flew a nine-month certification programme, and certification was granted on November 14, 1984. USAir received the first aircraft on November 28, and Southwest Airlines put the type into service that December.

The -300 was a commercial success: Boeing received 252 orders in 1985 alone and over 1,000 during production. Throughout the 1980s the Classic series attracted large orders from US and European airlines, exceeding the totals of earlier 737 models, and the -300 was by far its most successful member, with 1,113 deliveries against 486 for the -400 and 389 for the -500. Major operators included US carriers, small national airlines and charter carriers. Production lasted more than 15 years, until the last aircraft was delivered to Air New Zealand on December 17, 1999, registered ZK-NGJ.

Aircraft in service could be retrofitted with Aviation Partners Boeing winglets; so equipped the type is designated -300SP (Special Performance), which first entered service in June 2003. Others were converted into freighters. In December 2008 Southwest Airlines selected Boeing to retrofit its -300s with new instruments, hardware and software to improve commonality with the 737-700, but the order was later cancelled and the retrofits never took place. That same year, with fuel prices at a peak, United Airlines announced it would retire all 94 of its Classic 737s, including 64 737-300s. The -300s were typically retired after 24 years of use.

The model's most striking second life is aerial firefighting. Canada's Coulson Group modified six former Southwest Airlines 737-300s as air tankers, supported by a loan from the Canadian government: the 737 FireLiner carries 4,000 US gal (15 m3) of retardant and retains 66 seats, and the first was completed in 2018 and deployed to Australia. In the Next Generation family the -300 was replaced by the 737-700.