Boeing 737-300

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By the 1980’s, the Boeing 737 had cemented itself as one of the most reliable and useful passenger aircraft in the world, with hundreds of these machines plying their trade across the globe. However, it was at this point that the previous design, the 737-200 of 1967, was starting to look its age, and thus Boeing began work on both a replacement and an expansion. Thus enters the first of what was to be later dubbed the 737 Classic series, the 737-300.

The 737-300’s roots extend back as far as 1979, when it was decided by Boeing that the 737 series needed an aircraft of increased range, fuel efficiency, capacity and reduced noise output. The most important feature Boeing desired for their new 737 variant was improved engines. While engines on the 737-200 Advanced had been successful at their task, the technology behind them dated back to the early 1960’s, being, for all intents and purposes, engines from the 727 Trijet that had just been slung under the wings. For this task, Boeing turned to CFM International, a joint venture between GE Aviation, a division of General Electric of the United States and Safran Aircraft Engines (formerly known as Snecma), a division of Safran of France. The venture had been founded in 1974 in order to develop the new CFM56 high-bypass turbofan aircraft engines. CFM, however, had a problem, their engines weren’t selling. Upon the launch of the engine, no new models were being produced that could either accommodate or required the CFM56 engines, and their lack of brand recognition, as well as their position outside the USA, meant they were hard to market. Initially, the only orders the company got were by the USAF, in order to re-engine their fleet of Boeing KC-135R air-to-air tankers, as well as a small order for re-engined Douglas DC-8’s by some airlines.

The company was on the brink of folding when, by the grace of God, Boeing stepped in. Impressed by the performance of the CFM56 on the reworked KC-135’s, the

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The 737-300 prototype during its maiden flight.

company chose this engine to be the main powerplant for their upcoming, upgraded 737. However, before the CFM56 could be added to the 737, it had to undergo some structural modifications. Because the 737’s wings are so low to the ground, the normal, circular cross-section was ‘squashed’, making it more compact and allowing for suitable ground clearance. The fan diameter was reduced, which reduced the bypass ratio, and the engine accessory gearbox was moved from the bottom of the engine (the 6 o’clock position) to the 9 o’clock position, giving the engine nacelle its distinctive flat-bottomed shape. The overall thrust was also reduced, from 24,000 to 20,000 lbf, mostly due to the reduction in bypass ratio. With the CFM56’s, the new 737-300 was given a range of 2,255nmi and could fly at a cruising speed of 430 knots.

Aside from the engine, the 737-300 took many design features, such as the aerodynamic, structural, cockpit and cabin features, from Boeing’s long-range projects, the 757 and the 767. Even so, the aircraft still shares 67% of its parts with the previous 737-200. Also the aircraft was designed to have similar flying qualities, cockpit arrangements and procedures to minimise training differences and permit a common type rating. The most notable changes to the 737-300’s body were a 44 inch lengthening forward of the wing, and a 60 inch lengthening aft of the wing. Composite materials were used on all flight controls to reduce weight and aluminium alloys used in areas such as wing spars, keel beams and main landing gear beams which improved their strength by up to 12%, thereby increasing service life. The wings were extensively redesigned to enhance low speed performance and cruise efficiency.  The chord of the leading edge outboard of the engines was extended by 4.4%, this reduced the wing upper surface camber forward of the front spar to increase Mcrit thereby giving better transonic airflow characteristics and

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A KLM Boeing 737-300 on the taxi.

improved buffet margins. The span was increased by a wingtip extension of 11in. These two changes had the greatest impact on high speed performance and as a result, the turbulent air penetration speed changed to 280 Knots.

High lift characteristics were also enhanced by re-sequencing the slats and flaps. The leading edge slat radius was also increased which gave a 2.5kt reduction in Vref over a -200 at the same weight. Other changes to the wing structure included strengthened materials and corrosion protection. Rumour has it that the fin was also “given” to Shorts for use on their SD-360 as a reward for their good contract work for Boeing. Whether this is true or not, the SD-360 fin certainly looks identical, albeit scaled down.

Development of the 737-300, as mentioned, began in earnest in 1979, and by 1980 the general specifications of the aircraft were made public at the Farnborough Airshow so as to attract potential buyers. The project was officially launched in March 1981, following 10 orders from both USAir and Southwest Airlines, with an option for 20 more. The prototype was eventually rolled out of the 737 factory at Renton on January 17th, 1984, and flew on February 24th the same year. After exhaustive testing throughout the year, the FAA granted it certification on November 14th, and the first aircraft was delivered to USAir 18 days later. The success of the design, including increased fuel capacity, speed, range, efficiency and capacity, combined with reduced noise, made the 737-300 a very popular airliner, with 1,113 being delivered before production ended in December 1999. Pretty much every single airline on earth ordered or has used the 737-300, with major carriers including British Midland, American Airlines, USAir, Southwest Airlines, SABENA, Air France, Lufthansa, LOT Polish Airlines, TAP Portugal and so on.

However, the 737-300 has, like many great aircraft, sadly been marred with tragedy, suffering 15 incidents resulting in 757 fatalities.

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A 737-300 in the employ of Aegean Airlines.

The first incident involved TACA Flight 110 on May 24th, 1988. While en route to New Orleans, the aircraft suffered double engine failure due to a severe hail storm, resulting in the pilots being forced to land on a grass levee on the banks of the Mississippi with no injuries. As a result of this incident, further engine development was carried out to prevent flame-out in severe weather conditions.

The first fatal incident occurred on May 11th, 1990, where a 737-300 being towed to the runway at Ninoy Aquino International Airport in Manila, suffered an explosion in the central fuel tank and was consumed by fire in under four minutes, killing 8 passengers. It is thought the vapours ignited due to damaged wiring, as no bomb, incendiary device or detonator had been found at the scene. The airline had fitted logo lights after delivery which required passing additional wires through the vapour seals in the fuel tanks. The NTSB recommended to the FAA that an Airworthiness Directive be issued requiring inspections of the fuel boost pumps, float switch and wiring looms as signs of chafing had been found.

Among the worst incidents, and one that called into question the operational efficiency of air traffic controllers, was USAir Flight 1493, which, on February 1st, 1991, landed on top of a SkyWest Airlines Fairchild Metro III at Los Angeles, resulting in the deaths of all 12 people on the Fairchild Metro and 20 passengers and two crew members on the 737. The cause was found to be the air traffic controller being distracted by the busy LAX rush hour traffic, and accidentally allowed the Fairchild Metro onto the runway before leaving it in the direct path of oncoming aircraft.

However, during the 1990’s, a series of horrendous crashes almost resulted in all 737’s being grounded. The first involved United Airlines Flight 585, a 737-200 which crashed on approach to Colorado Springs Municipal Airport in 1991 after an uncommanded rudder hardover, killing all 25 aboard. On September 8th, 1994, USAir Flight 427, a 737-300, was struck by an abrupt an uncommanded rudder hardover while landing at Pittsburgh International Airport, resulting in the deaths of all 132 aboard. On June 9th, 1996, while the NTSB’s investigation of Flight 427 was still ongoing, the pilots of Eastwind Airlines Flight 517 briefly lost control of their aircraft while flying from Trenton, New Jersey to Richmond, Virginia. The aircraft experienced two episodes of rudder reversal while on approach to land in Richmond. Unlike the two prior incidents, the rudder issues on Flight 517 spontaneously resolved and the pilots were able to safely land the aircraft, and none of the 53 people aboard were injured. The National Transportation Safety Board ultimately determined that the accidents and incidents were the result of a design flaw which could result in an uncommanded movement of the aircraft’s rudder. The issues were resolved after the NTSB identified the cause of the rudder malfunction and the Federal Aviation Administration ordered repairs for all Boeing 737 aircraft

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A 737-300 in the colours of United Airlines subsidiary, Shuttle by United, a short lived domestic venture that lasted from 1994 to 2001.

in service.

The painful memories of these rudder incidents were again brought up following the crash of SilkAir Flight 185 on December 19th, 1997. The flight, while operating from Jakarta to Singapore, suddenly dove from its cruising altitude of 35,000ft to the ground in less than a minute, crashing into the Musi River in rural Indonesia killing all 104 aboard. While the airline blamed a PCU fault that caused the sudden rudder hardover, the NTSB had reason to believe it was an act of pilot suicide. As of 2017, the cause of the crash has not been determined.

As mentioned, the 737-300 remained in production until December 1999, the last unit being delivered to Air New Zealand. The aircraft was replaced in the product listing by the 737-700, but even today older models are still in frontline service with many large airlines, with modifications still available. For instance, the 737-300 can be retrofitted with Aviation Partners Boeing winglets to improve fuel efficiency and performance, these being designated the -300SP (Special Performance). The -300 is also a popular aircraft for conversion into freight and parcels operations. Here in the UK, 737-300’s are flown on behalf of Royal Mail for postal flights across the British Isles and to mainland Europe. As of 2016, 483 737-300’s are known to still be in active service, with even the launch customer, Southwest Airlines, still being in possession of 107 of these aircraft, though plans are to retire the whole fleet of -300’s by September 2017, replacing them with the latest 737 model, the Boeing 737 MAX 8.

Overall, the 737-300 is an aircraft that has truly stood the test of time. 33 years after the first ones left the factory, many of these birds continue to do what they do best, thanks to their endless reliability, their efficiency, their speed and their comfort. While the 737-200 had more units built, the inefficiencies that the -300 came to replace are what consigned many, even the later ones from the 1980’s, to the history books, while even the earliest -300’s from 1984 and 1985 are still a major player in the operations of so many important airlines across the globe.