, the earliest production variant of the 707
Early history was a proposal for a quadjet fighter aircraft Prior to the
Jet Age, airliners were powered by
piston engines. Engine failures were relatively common, so providing redundancy with four engines was important for long range flights. This need extended into the beginning of the Jet Age, and combined with the limited thrust available from early
jet engines, it was most practical to design large jet airliners with four engines. The first commercial jet aircraft was the four-engined
De Havilland Comet, which first flew in 1949. This greatly tarnished its reputation and it was the later airliners that truly benefited from the subsequent improvements. In 1958,
Boeing introduced the
707 and a year later,
Douglas rolled out its
DC-8, both types also with four engines. Both were very successful and the 707 in particular is credited with advancing the Jet Age. The large airliners flourished during this period, frequently operating on both domestic and international routes.
Later decades and gradual decline By the 1960s it became apparent that having four engines reduced fuel efficiency. This was not an issue for long-haul routes which carried 300 or more passengers for 8 to 12 hours, allowing for a high cost-to-passenger-mile ratio. On the other hand, the large four-engined types were less suited for frequent short-haul services, which demanded multiple take-offs and landings daily, costing more fuel while also typically carrying fewer passengers per flight. This prompted the development of large
trijets and
twinjets. Due to limitations in engine technology, twinjets of this era were small and had relatively short range. The
FAA's 60-Minute Rule also prevented them from flying farther than 60 minutes away from diversion airports due to their lower engine redundancy. Trijets represented a compromise between fuel efficiency and redundancy. In 1969,
Boeing launched the
747. Nicknamed the "Jumbo Jet", it was the first
wide-body airliner, able to carry significantly more passengers than any other aircraft. Its capacity and performance were unmatched, even after the launch of wide-body trijet competition in the form of the
McDonnell Douglas DC-10 and
Lockheed L-1011 TriStar. on landing, showing its four underwing mounted engines.|left Within its own category in commercial aviation, the
supersonic airliner
Concorde began service in 1976. Its four
Rolls-Royce/Snecma Olympus 593 turbojets allowed it to cruise at twice the speed of sound. When the
BAe 146 was introduced in 1983, it was unusual because it was a four-engined short range
regional airliner. Its design ultimately enabled quieter operation and
short take off and landing capabilities. In the 1980s, the increased reliability and available power of
jet engines enabled twinjets to safely fly on one engine. This prompted the introduction of
ETOPS ratings for twinjets, allowing them to circumvent the 60-Minute Rule and fly on transoceanic routes previously serviced by four-engined types. The advantage of redundancy brought by four engines was no longer necessary and they could no longer compete with the lower fuel consumption and maintenance costs of twinjets with higher-powered engines. All but the largest four-engined types, such as the Boeing 747, became uneconomical and this led to the retirement of the ageing
707 and
DC-8 fleets for passenger service. Nonetheless, Boeing rolled out the
747-400 in 1989, which enjoyed high capacities (over 300 passengers) and long range, a combination still unmatched by twinjets at the time, making this the most commercially successful 747 variant. Airbus, after ending collaboration talks with
McDonnell Douglas who went on to produce the
MD-11 long-range trijet, instead launched the
A340 quadjet in 1993 as a long-range derivative of the
A330 twinjet as their initial variants shared the same fuselage and wing. can almost match the capacity of the largest four-engined types with superior efficiency. intended to introduce the four-engined
A340 for long-haul flights and the
two-engined A330 for shorter routes. While the A330 itself has evolved to be more capable of long-haul flights (especially with the latest
A330neo), the A340 has quickly been phased out in favor of more efficient two-engine solutions like the
Boeing 777 or its direct successor
Airbus A350. Between the 1970 and the 1990s, twinjets, trijets, and quadjets shared engines of similar output, such as when the DC-10, MD-11, Boeing 767, and Airbus A300, A310, and A330, and Boeing 747 all had variants powered by the widespread
General Electric CF6, so at the time additional engines were needed for larger capacities and longer range. The major advantages of three and four engines became much less significant when the twin-engined
Boeing 777 was introduced in 1995, equipped with the purpose-designed
General Electric GE90 engine developed from further advancements in high-bypass turbofan technology. The original
777-200 could seat upwards of 300 passengers, a significant increase upon existing twinjets such as the
767, which could typically only seat 200-300 passengers. The subsequent development of the
777-300ER pushed the passenger capacity to just under 400, approaching the
747 and superseding the
A340, while being more efficient and incurring lower engine maintenance costs. Airbus, not seeing much success with updated A340-500/600 variants powered by the
Rolls-Royce Trent 500, went for the all-new
A350XWB to compete against the 777 and
787 Dreamliner. By the early 2000s, the only remaining advantage of the largest types was their ability to carry more passengers than the largest twinjets. In the years following the
September 11 attacks, the increase in fuel prices and decline in the aviation industry heightened the need to minimise operating costs and expenditures. Production of the
747-400 passenger variant ceased by 2005 and deliveries of the
A340 dropped to 11 per year, as they faced competition from more efficient and comparably capable twinjets.
Current status Airbus A380 in special livery. The A380 is the world's largest airliner. The use of four engines was invigorated in 2005 when Airbus introduced the
A380, currently the world's largest airliner. It was designed for routes with ultra-high demand, typically seating 575 passengers in two full-length decks. However, as of 2018, Airbus has only fulfilled a quarter of its initial projected figure of 1,200 sales over two decades. This can be attributed to a modern trend towards
point-to-point travel using smaller but highly efficient twinjets such as the
Airbus A350 and
Boeing 787, as opposed to a
spoke–hub model which favours massive aircraft such as the A380. The largest operator of the A380,
Emirates, profits from its fleet because its primary hub is situated at
Dubai International Airport, where many long-haul routes have their stopovers. This makes it easier for Emirates to fill the seats of its A380s. The 747-8I passenger variant has only received 50 orders , while the 747-8F freighter variant has been more successful with over 100 orders. , the 747-8F is unmatched in range and payload, making it an option for cargo carriers. After the Airbus A380 ended production, the Boeing 747-8 also stopped production with the last delivery taking place on January 31, 2023, meaning no double-deck passenger jets were any longer in production. Boeing attributed the retirement of their 747 fleets to the effect of the COVID-19 pandemic. == Types currently in production ==