In direct correlation to my earlier article regarding the death of the trijet commercial airliner, the drive to create more efficient and economically sound jet aviation has also resulted in the gradual decline of the once revered quadjet. While a few stragglers remain, the number of jet airliner models with four engines has been largely rendered extinct in the wake of increased environmental concerns, fuel costs and the technology behind more efficient twinjets.
The idea of fitting four engines to an aircraft was a very early concept done largely for the sake of redundancy. As early powerplants were complex, inefficient and unreliable, the only thing many designers could do was to give an aircraft as many engines as possible to both increase the performance and as a backup in case of a failure. Some of the more exuberant designs of aircraft, including certain early flying boats, had up to eight propeller engines, but these designs were short lived and never truly went into full-scale production.
Four engines was deemed the happy medium for most designers, the first aircraft to be fitted with this configuration being the Sikorsky Russky Vityaz of 1913. World War I and the rise in aviation influence quickly saw development in aircraft technology expand, and soon four-engined aircraft were a common sight above the bloody fields of the Somme and Ypres. Aircraft including the Zeppelin-Staaken R.VI and the Sikorsky Ilya Muromets were, for the time, the pinnacles of aerial might.
It was after World War I that the era of the four-engined airliner truly kicked off, thanks largely to the Flying Boat concept. Due to a lack of range and reliability for land-based aircraft, as well as there being very few airports, the Flying Boat basically gave a small ocean liner wings and allowed it flexibility and performance as yet unheard of. The likes of the Short S.8 Calcutta and S.25 Sunderland, as well as the American Boeing 314 Clipper, proved that flying across the oceans of the world could be done quickly, reliably and in luxury akin to the magnificent steamships and liners which had preceded them.
However, even land based four-engined designs were being innovated to increase their range and their reliability, with the likes of the Focke-Wulf Fw 200 Condor and the Boeing 307 Stratoliner proving the concept. Gradually, the improvement of land-based aviation, including major investments in airports and following the phenomenal success of the Douglas DC-3, would result in the era of Flying Boats being consigned to the history books.
It was thanks to World War II that major developments in the field of aircraft technology were advanced in leaps and bounds. This horrific conflict, which claimed the lives of millions of people across the globe, was the first true demonstration that aerial superiority was the modern way in which tactical victories could be achieved efficiently and quickly. As such, development of aviation technology resulted in a slew of various designs which were at the cutting edge; introducing to the world to improved engine design, cabin pressurisation, advanced avionics and many more aircraft design components we take for granted today. As a result, it was almost an industry standard for commercial airliners in the late 1940’s and 50’s to be universally four-engined aircraft, both to replicate the power and performance of legendary WWII bombers, but once again to provide redundancy in the event of powerplant failure. The likes of the twin-prop Douglas DC-3 were soon replaced by the magnificent Lockheed Constellation, Douglas DC-6 and DC-7 and the Boeing 377 Stratocruiser; all of which were quad-engined.
However, the war’s conclusion in 1945 also brought into focus the new direction aviation was going to be taken; the way of the turbojet. German fighters of World War II demonstrated that jet-power made flying faster, more efficient and more reliable. Therefore, aircraft manufacturers immediately leapt at the opportunity to create their first jet airliner and become undoubtedly the most advanced plane to ever take to the skies.
Even before the war’s conclusion, the United Kingdom had considered, as part of the Brabazon Committee, a range of commercial airliners that would be released following Hitler’s defeat; one of which was a long-range commercial jet airliner. This pioneering design, known as the De Havilland Comet, made its first flight on July 27th, 1949. The aircraft was fitted with four Halford H-2 Ghost 50 turbojets producing 5,000lbf each, whisking the airliner to a top speed of 460mph and a service ceiling of 42,000ft; absolutely unprecedented numbers in a time when trains still ran on steam!
13 days later, Avro Canada launched their own pioneering jet airliner design, the C102 Jetliner. This aircraft was again of a quadjet configuration, fitted with four Rolls-Royce Derwent 5/17 turbojet engines producing 3,600lbf each and pushing the aircraft to a top speed of 420mph and a service ceiling of 40,000ft.
The common factor between these two aircraft is the fitting of four engines. As this early turbojet technology had not been fully proven, redundancy was at the forefront of the designer’s minds. At the same time, these early jets didn’t allow for the power and performance of modern equivalents, meaning that twinjet options back then would’ve been down on power and range by comparison. The only twinjet design you could find outside of military aircraft in the 1950’s was the Sud-Aviation Caravelle of 1955, a French regional airliner which had neither the range of the Comet or the Jetliner, but was utterly reliable.
The advent of the Comet and Jetliner caught the Americans napping. In their preoccupation to destroy communism through a massive arsenal of fighters and bombers, they soon found that their flaky fleet of piston-powered propeller planes such as the Lockheed Constellation and the Douglas DC-4 were truly outmatched by the foreign jet-powered competition. America needed to catch up, and they certainly did it quick. By 1954, the Jetliner project had been scrapped due to Avro Canada’s requirement to provide fighters to help in the Korean War, while the Comet was in dire straits due to a series of horrendous accidents caused by the then unknown phenomenon Metal Fatigue.
In the same year, Boeing unveiled its first essential jet airliner, the Boeing 367-80; affectionately dubbed the “Dash 80”. This aircraft was spawned from a requirement by the USAF to provide them with a new transport and tanker aircraft, with the development of a passenger airliner being more a spin-off from this project. Putting the company’s future at risk, Boeing’s gamble paid off when, in 1958, America’s first jet airliner, the Boeing 707, was launched to widespread acclaim and universal adoration. This was followed in 1960 by the Douglas DC-8 and the Convair 880, which again utilised a quadjet configuration for both reliability and performance purposes.
Soon America had sown up the entire commercial aviation market, and for a brief period between 1958 and 1961, aside from the Sud Aviation Caravelle, the only airliners you could find flying by jet power had four engines. It was the age of the quadjet, but this is where the development of this technology truly hit the glass ceiling.
It became quickly apparent in those early days of jet aviation that aircraft with four engines weren’t exactly the most efficient forms of transport, nor were they the most flexible. Boeing’s first take on a domestic airliner, the Boeing 720, failed to endear itself to a widespread market due to the cost of operating four engines with lower passenger numbers. Quadjet powered aircraft work most efficiently on long-haul operations carrying upward of 300 passengers while cruising steadily at 43,000ft for upwards of 8 to 12 hours; allowing for a highly favourable cost-per-passenger-mile ratio. A short-haul flight on the other hand means there is a constant stop-start routine as aircraft frequently takes off and lands, costing more fuel to get the plane back into the air while also likely having fewer passengers than higher demand long-haul operations. This isn’t helped by the extra maintenance required for each additional engine; again, eating into the profits earned from passenger fares.
For a period, quadjet design in the west stalled, with the last two new four engined jet designs being the Convair 990 Coronado of 1961 and the Vickers VC10 of 1962. While four-engined designs continued in the Soviet Union during the mid to late 60’s, this was largely down to the unreliability of Russian engine designs and their poor performance. Perhaps the most notable case in point of this was the Soviet Union’s first wide-body jet airliner, the Ilyushin Il-86. Even with four engines, this aircraft was woefully slow and highly inefficient. The aircraft had been bungled through a seemingly endless trail of government interference and internal warring between different factions of the Politburo, while a lack of building materials and delays in designing a suitable engine for the aircraft, a problem that went unresolved throughout its entire production life, meant that the final product was incredibly underpowered and, for its size, only had the range of a middling Boeing 737. It really was like something out of the stone age, with its only saving grace being that, in comparison to other Soviet jets, it was a fairly reliable airliner; considering it was only held together by a thread!
In the west, however, twinjets and trijets had finally made their debut in earnest; twinjets included the Douglas DC-9, the BAC 1-11 and the Boeing 737, while trijets comprised of the Hawker Siddeley Trident and the Boeing 727. Each of these designs demonstrated higher levels of efficiency and ease of maintenance when compared to the equivalent quadjets; especially on domestic routes. However, domestic routes were the only place these aircraft could operate as once again turbojet design had not advanced to the point where a twinjet or trijet could perform in the same manner as quadjets on long-haul routes.
This was compounded further in 1969 by the launch of the first new quadjet commercial airliner, the Boeing 747. The much loved and culturally iconic Jumbo Jet took engine design to a whole new level in terms of providing performance, reliability and range. Very soon the aircraft had effectively brought commercial air travel to the masses, introducing a universal design that was simple, easy to maintain and could easily carry upward of 300 passengers in comfort and safety across thousands of miles. The 747 rewrote the book on commercial aviation design and other manufacturers scrambled to create a suitable competition. While McDonnell Douglas and Lockheed attempted to undercut the 747 with their more lightweight DC-10 and Tristar, hoping to exploit their ability to land at a wider range of airports with shorter runways, neither truly caught on in the same way as the 747. Whatever expense the 747 incurred in terms of operating as a quadjet was easily made up for by its sheer passenger numbers and range, making the trijet competition superfluous by comparison.
However, in 1972, the canker that would eventually be the undoing of both trijets and quadjets in the decades following lifted off from a small airport in Toulouse; it’s name, the Airbus A300. The A300 was the world’s first long-haul twinjet, a smaller design than the 747 but infinitely more efficient and easier to maintain. The brainchild of the combined efforts of European aircraft manufacturers, the A300 was a highly advanced piece of aviation equipment and would soon carve out an ever increasing niche for itself across the globe, including in the USA.
Regardless of the 747’s success, though, it did not usher back in the age of the quadjet. Engine reliability had been upped and thus the requirement for having four engines on an airliner was less of a concern. The 747 only needed its four engines to help propel its huge airframe and compliment of passengers and freight skyward, less as redundancy in the event of failure. In fact, the only other long-range quadjet airliners that took to the sky during the 1970’s were the aforementioned Ilyushin Il-86 and the Aérospatiale-BAC Concorde. The Il-86 failed for the various reasons stated above and was barely able to fly outside of its Soviet home, let alone become a successful jet airliner. As for Concorde, while this was the world’s first supersonic passenger aircraft, the incredible cost of operating it meant that it was never able to make back its money on ticket sales. This was compounded by numerous opposition regarding noise and damage caused by sonic booms, resulting in only 20 aircraft being built and only operated by two airlines.
The 747’s woes were further compounded, to a moderate degree, by the fuel crisis of 1973. The sudden spike in fuel costs made the aircraft, which had become the flagship of many major airlines, an unattractive buy; stunting sales. The expense of operating quadjets was so great that American Airlines, who operated a sizeable fleet of 747-100’s, replaced them after only four years by the Douglas DC-10 trijet (for good or for ill). 747’s were relegated to cargo roles before being fully retired in 1984, with one example becoming a carrier aircraft for the Space Shuttle.
Other major carriers avoided the 747 entirely, including the likes of Eastern (who opted for twinjet A300’s and trijet Tristars).
Full reliance on quadjets was also the beginning of the end for many classical carriers, most notably Pan Am. The airline, by 1973, had a fleet comprised almost entirely of 707’s and 747’s, which had now become massively expensive to operate and their overall profit margins began to suffer. While the airline managed to redress the balance somewhat, its financial stability had been knocked off centre and the company would fight a losing battle against its own operational costs right up until its eventual closure in 1991.
However, there was one more quadjet design that made its debut during this period and that was the plucky Brit simply known as the British Aerospace 146; better known to you and I as the BAe 146.
The BAe 146 was unusual in that it was a domestic airliner fitted with four engines as opposed to the more conventional two or three. This largely came down to the fact that the aircraft was to become the world’s first Short Take-Off and Landing (STOL) jet aircraft. In order to perform adequately, it needed small engines which were sourced from the Bombardier Challenger business jet of 1978. However, during the design process, it was found that in order to help get the 146 into the air on the short runways from which it would be operating, an extra pair of engines were needed to lift the extra weight of the airframe and passengers. The result was an incredibly efficient four engined jet airliner that could take off and land on less than 3,000ft of runway and was as quiet as a mouse while doing so; earning the aircraft the nickname “Whisperjet”. As such, the 146 and its derivatives became a major part of the up and coming regional jet trend of the early 80’s which saw small, inner city airfields opened up to commercial air travel; making it the most commercially successful British jet airliner ever.
Otherwise, the 1980’s and 1990’s saw many of the original quadjets come to an end. By 1990, the Boeing 707 and Douglas DC-8 had been relegated to either the scrapyard, third world nations or freight operations, while the Convair 880 and 990, as well as the VC10, had disappeared from civilian use entirely. It was only the immense sales success of the Boeing 747 and the BAe 146 that kept the quadjet alive during this period. However, the launch of the highly advanced Boeing 747-400 in 1989 reinvigorated interest in four engined jet airliners. The -400’s mixture of fuel efficiency, range and performance made it the absolute pinnacle of commercial aviation technology and a must-have airline accessory. The aircraft sold like hotcakes and pretty soon a majority of the remaining manufacturers were proposing their own similar designs.
In 1993, Airbus launched the A340, the company’s first four engined jet airliner and a perfect mixture of capacity, efficiency and technological prowess. Meanwhile, McDonnell Douglas intended to launch a four engined, double-deck airliner known as the MD-12, scheduled for launch sometime in the mid to late 1990’s. However, the failure of the company’s MD-11 trijet to recoup its development costs meant that the manufacturer was haemorrhaging money and eventually found itself being merged into Boeing in 1997.
The 747 and the A340 became extremely successful aircraft, thanks largely to the fact that, while twinjets were much more efficient, they simply had not the capacity to compete with the four engined behemoths. Any losses incurred by using a quadjet were covered by the number of passengers the plane could carry, and with the added bonus of their efficiency these further reduced their operational expenditure. Fuel was cheap, the economy was good and these two aircraft had become the poster children of the aviation industry in the 1990’s, but all that was about to change radically in favour of the twinjets.
The first signs of trouble came in 1995 when Boeing launched the 777, their largest twinjet design to date and an immediate sales success. Two years earlier, Airbus had released the A330, which was comparable to the likes of larger Boeing 767’s; not an immediate sales success but eventually gathered pace within the industry. At first, the 777 and A330 seemed like variations on earlier themes regarding large, wide-body twinjets with nothing particularly noteworthy about them apart from their highly advanced technology and incredible efficiency.
However, as different versions of the aircraft were released throughout the late 90’s and early 2000’s, namely the 777-300ER and the A330-300, their ability to combine capacity and fuel efficiency, especially following the stagnation of the aviation market in the post-9/11 world, meant they were soon starting to make inroads into the dominance of the 747-400 and A340.
The increase in fuel prices and reduction in revenue in the years after September 11th, 2001, meant that airlines had to trim the fat from their expenditure in any way possible. While many carriers fell victim to the market crash early on, such as Sabena, Ansett Australia and Swissair, other airlines had to undertake a major fleet overhaul by retiring either old or inefficient models and implementing fleet standardisation. Both trijets and quadjets were expunged from the rosters, being replaced by a slew of younger but far more efficient and better performing counterparts. However, rather than buying the likes of the Airbus A340 or 747 to replace their ageing rivals, airlines instead opted for twinjets like the 777 and A330.
The result was the demand for quadjets and subsequent sales plummeting. The 747-400 was hit particularly hard, going from 27 deliveries in 2002 to 19 in 2003 and 15 in 2004. This model would eventually be retired from production in 2005 for passenger operations, but did maintain a sales presence for the freight sector until 2009.
The A340, however, saw some modest success through the creation of further variants. The A340-500 and A340-600 modified the design to satisfy certain market demands for range and capacity; the -500 being the longest range commercial airliner ever built at the time and the -600 having the longest fuselage ever put on an aircraft in history.
However, while the -600 was able to find a home with some major carriers due to its immense capacity, the -500 was utterly trounced as it endeared itself far too much to a niche market. Sales of the original A340-300 on the other hand dropped like a rock, falling from 22 aircraft delivered in 2001 to 8 in 2002. Overall sales fell from 24 in 2006 to 11 in 2007, with the costs of the 2008 economic crisis only serving to stunt the aircraft’s deliveries further. The A340 would eventually end production in 2011 in the face of dismal sales. Airbus had originally forecast sales continuing to 2016 with upward of 120 units delivered. Instead, for the 2005 production year, 155 Boeing 777’s were sold in comparison to only 15 A340’s.
By 2005, it seemed that the quadjet was soon to be a thing of the past. The 747-400, at least the passenger variant, was gone and the A340 was stuttering along, barely able to keep its head above water. However, in that same year, the heart of the quadjets, like it had been in 1989 with the 747-400, was restarted by the launch of the Airbus A380 Superjumbo; a double-deck behemoth that became the largest commercial airliner ever built.
The Airbus A380 was over 10 years in the making, but, in spite of all the economic and environmental factors levelled against it, Airbus persevered and saw it through to production. Though construction of the A380 is a logistical nightmare for the company, with parts having to be shipped from all across Europe by archaic barges and on the backs of flatbed lorries through narrow French streets, the company has made the A380 the epitome of the modern aviation industry and what is physically possible with regard to getting so much into the air in comfort and style.
The Airbus A380 has truly become a fashion statement of the airline industry, which is good because it otherwise has no practical value in this day and age.
The aircraft’s bold statement is truly the only reason airlines elect to buy and operate them. While it is able to carry double the number of passengers of the A330, its operating costs are also doubled, which means that for less cost to the carrier the same amount of passengers could just as easily be transported by operating two A330 flights in place of the one A380 flight. Emirates, the flag carrier of the United Arab Emirates, possess by far the largest fleet of these Superjumbos in the world, but these are again only to show off the nation’s wealth with regard to operating these giants. In the real world sadly, the operation of multiple A380 flights on the same route per day results in these planes operating nowhere near full capacity. This isn’t unknown to these carriers, which is why they trade what would otherwise be empty economy seats for luxury suites and private staterooms; akin to the lavish flying boats of the 1920’s and 30’s. The A380 doesn’t operate at a loss in this respect as they can simply charge wealthy passengers a fortune to fly in ultra-luxurious conditions to make up the shortfall.
The A380’s lack of practical significance was truly emphasised early on when variations of the aircraft, the A380-900 and the A380-800F were cancelled before they got the concept stage. The -900 was to be an even longer version of the A380 with a capacity of 650 passengers, the equivalent of two Boeing 777’s, while the A380-800F was a cargo variant which was endeared to freight operators such as UPS and Fedex.
However, the -900 was nipped in the bud when sales for the A380-800 stalled during its formative years. Though many large carriers showed interest in the -900, the recession of 2008 meant demand was low and the project was scrapped in 2010; although there are rumours that Airbus are once again investigating this particular avenue of thought.
As for the -800F, while it boasted the second highest freight capacity for a jet aircraft, second only to the Antonov An-225, it was deemed cost prohibitive by most carriers, who instead opted for buying converted MD-11’s and 747’s.
As of 2018, the A380 has only sold 226 units and current sales forecasts consider the aircraft to have plateaued for the time being. Such is the lack of confidence in the aircraft’s economic future that the A380neo (New Engine Option) was cancelled, instead being given to the 25 year old Airbus A330 design. The only significant upgrade to the A380 is the ‘plus’ project, which considers a modified winglet design to improve efficiency.
However, while Airbus have only just been able to keep their quadjet afloat, Boeing have failed abysmally!
In 2011, the company released the much belated successor to the 747-400, the Boeing 747-8. The -8, which came in the -8I (Intercontinental) passenger and -8F cargo versions, was built to show the world that the 40 year old 747 still had some viability left in it and would become a true competitor to the Airbus A380. However, apparently their market research team had failed to notice the state of the aviation industry in the years since the 747-400 as the aircraft has completely bombed in terms of deliveries.
When the 747-400 was launched in 1989, the economy was good and there were no viable competitors at the time which could combine the aircraft’s efficiency and capacity. When the 747-8 was launched in 2011, there were a slew of comparable models which were both younger in design, equal in capacity and far more efficient, including several of Boeing’s own products like the 777-300ER and the 787, as well as the A330 and A350XWB. To exacerbate things further, the unstable global economy and the ever increasing rise in fuel costs and environmental considerations have only helped to further cripple the 747-8’s sales.
While the freighter variant saw early success initially, the passenger version has never truly had its day in the sun and its doubtful it ever will. Boeing announced its intention to slow production to 0.5 aircraft per month on all models following the stagnation of the air freight market in 2016. While prospects for the 747-8F are expected to turn for the better by about 2019, the outlook is still fairly gloomy, especially for the 747-8I. At the same time, Boeing have proposed a new variant of the 777; the 777X range. These include the 375 seat 777-8 and the 425 seat 777-9, both of which have garnered a slew of solid orders from airlines globally.
As such, Boeing have expressed doubts in the future of 747 production, and while there are currently 138 orders on the cards a majority are for the freight version; with 88 747-8F’s being ordered against 50 747-8I’s. Today, only 6 airlines operate the 747-8I, while 10 operate the -8F, and even then the airlines with the highest numbers on their books are the launch customers. Boeing couldn’t even get British Airways on board, and they’ve been avid 747 buyers since the days of BOAC in the early 70’s; instead opting for 787’s on the long distance routes and using the A380 as a fashion statement everywhere else.
Therefore, in light of these forecasts, the future of the quadjet does look sadly bleak. Both of the remaining four engined designs are slow in the sales department and their respective builders have no intention to create improved variants to try and reinvigorate interest.
Simply put, the quadjet is an unfortunate throwback to days gone by. Its original intention was as a means of redundancy in the face of the unreliable and underperforming powerplants of the time, conceived through necessity more than anything else. However, as the aviation world has moved on the quadjet has remained stuck in the past. Engine reliability, performance and efficiency have improved tremendously, while airliner design now accounts for models of equal capacity using only two engines rather than four. Today, aside from the brand new quadjets like the A380 and Boeing 747-8, quadjets are slowly becoming a fading memory of more prosperous times for the airline industry.
Aircraft graveyards such as Mojave, Kemble and Lourdes have now become the final resting place for the rusting hulks of Boeing 747’s and Airbus A340’s, their second-hand economic value being so low they’re practically worthless. Those that remain in service are slated for retirement, with even the most dedicated quadjet carriers, including British Airways, Lufthansa and Air France, planning to retire their four engined fleets by the end of the decade. A340’s are particularly tragic, as many of the units scrapped were barely run in, some being as young as 8 to 10 years old.
The truth is, if you’d asked me when I was a kid if the likes of the 747 or A340 would ever disappear from the skies forever, I’d have told you never. But sadly I do believe this is finally the case. Economics and time have caught up with the quadjet and now its on its slow and sorry slide to its inevitable end.