With the ongoing retirement of the Boeing 747-400 and the end of production of the Airbus A380, there is no doubt four-engine aircraft are falling out of favor. Twin-engine aircraft have improved significantly, and many airlines are moving away from the high-capacity ‘hub and spoke’ model. It seems unlikely there will be a need anytime soon for a four-engine passenger aircraft, but perhaps it could re-appear for freight.
The growth of the quadjet
Four engines were how the jet age started. The de Havilland Comet was the first jet aircraft to be introduced in 1952, and the Boeing 707, which came soon after in 1958, was the first to really become successful (and profitable). The 747, which followed in 1970, was another gamechanger, using four higher-powered engines to increase passenger capacity significantly, and change the economics and possibilities of passenger aviation.
Twin engines, of course, have worked for smaller aircraft. The Boeing 737, launched in 1967, was Boeing’s first (following the four-engine 707 and three-engine 727) and has gone on to be the most sold aircraft to date. Four engines have remained for some aircraft, though, including the Airbus A340 and A380.
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Improvement in twin-engine aircraft
Four engine production has declined as twin-engine operations have improved. In the early days of jet aircraft, a twin-engine aircraft (under FAA rules) could not fly more than 60 minutes away from a diversion airport. This hugely limited the possibilities for trans-oceanic flights.
This changed with the introduction of ETOPS (Extended-range Twin-engine Operational Performance Standards) in the 1980s, with the Boeing 767 being the first twin-engine to be rated to 120 minutes. This has continued to improve, with the Airbus A350, for example, rated 370 minutes.
Along with this improvement in ETOPS, engine power has also increased. A 1958 Pratt & Whitney JT3D engine on the 707, for example, had a thrust of 17,000 pounds, versus the GE9X engine on the 777X with around 105,000 pounds of thrust. Manufacturers can now power large single-deck widebodies with two engines.
Airlines have shifted to twinjets
These improvements have seen much larger twinjets take over the four-engine territory. Where four engines are still needed is with heavy airframes. Airbus, of course, has tried to make this work with the A380. A great aircraft, but it has failed to work for many airlines.
It is expensive to operate, and for many routes, it makes sense to schedule multiple smaller aircraft (offering more flexibility in schedules and more freight capacity) rather than one massive one.
Four engines may even be too much for any future supersonic travel. Concorde used four engines, but designs for the potential Boom Overture supersonic transport are for three engines.
A possible use for freight?
It seems unlikely that airlines will see a need for a heavy, high-capacity passenger aircraft that would require four engines again any time soon. The higher operating cost cannot be justified, especially when many don’t need the considerable passenger capacity, and while the ‘point to point’ operating model remains preferable to ‘hub and spoke.’ The slowdown in passengers in 2020 increases the chances this will stay the same.
Where four engines, and high capacity, may be seen is in freight use. The Boeing 747 has been one of the most successful freight aircraft ever made (the 747 and 777 dominate freight operations today), and there has been a strong interest in the 747-8 freighter version.
There is talk of a 777X freighter version from Boeing, bringing the fuel efficiency and other advances of this new aircraft to freight operations. And the Antonov 225 (with six engines and capacity far exceeding the A380) still finds use for heavy freight.
With the 777X possibility and the ongoing 747-8 production, any new four-engine development even in this area seems unlikely but still more likely than for passenger use. Remember that Airbus did at one stage have plans for an A380 freighter, but this was dropped.
What do you think? Will we see another four-engine aircraft developed, and for what use? Let us know your thoughts in the comments.