In the past, it wasn’t uncommon for air travellers to find themselves being ferried from place to place on jet airliners fitted with three engines. The 1960’s and 70’s were truly the era of the Trijet, with craft such as the DC-10, the L-1011 Tristar and the Boeing 727 being icons of this pioneering episode of aviation history. However, things suddenly went disastrously wrong for this type of airliner, the Trijet becoming very much a victim of circumstance before disappearing almost completely by the turn of the new millennium.
Contrary to popular belief, the world’s first Trijet was not the Hawker Siddeley Trident of 1962, but was in fact the Soviet Union’s Tupolev Tu-73, a prototypical jet fighter built in 1947. However, it’s impact on aviation is comparable to its flying career; in that it didn’t have one!
Regardless, the Hawker Siddeley Trident of 1962 was the world’s first successful three-engined jet aircraft, as well as the world’s first T-Tail jet airliner design.
The concept behind aircraft with three engines was done as a contingency against the unreliability of early turbofan jets, as well as to increase range. Prior to the Trident, aircraft such as the Boeing 707 and the de Havilland Comet were fitted with four engines, but their size and weight precluded their ability to use certain airports with shorter runways. Early designs, such as the Trident and the 727, were built to the specific standards ordered by their customers. In the case of the Trident, the aircraft was configured to suit the needs of BEA (with the inclusion of the innovative if expensive Blind-Landing system), while the Boeing 727 was a more universal design tailor made for as many airlines as possible by keeping the principles comparatively simple.
Overall, the advantages of a Trijet system over the likes of quad and twin-jets were largely down to the way the aircraft was configured. To compliment the engines being placed rearward, the wings were located further back as well to provide the highest amount of lift at the area of most weight (where the engines are). As such, the centre-of-gravity for Trijets was much further back, allowing for a lower rotation speed.
The movement of the engines to the rear of the fuselage also reduced drag, especially on the wings. With a ‘clean-wing’, the large engine-pods were no longer present to disrupt the aerodynamic flow of the aircraft in the same manner as twin-jets and quad-jets.
The main advantage the Trijet had over the quad-jet came largely down to fuel efficiency and maintenance costs. A Trijet could produce equal amounts of power to a quad-jet, but at a reduced price in terms of both fuel consumed and the number of engines which would need to be maintained. In the early days, jet engines were cumbersome and difficult to manage, thus a reduced number of engines made it much easier for airlines to maintain their fleet and have their aircraft back in service in shorter amounts of time.
While twin-jets had the advantage of costing less to maintain and operate, in 1962 there were no engines powerful enough to give them a competitive range. The Sud Aviation Caravelle was the world’s first twin-jet airliner, followed closely by the BAC 1-11 and the Douglas DC-9, all of which were only regional jets with a range of less than 2,000 miles. It wouldn’t be until the early 1970’s that a suitable turbofan engine would be developed to give Twin-jets the range they needed.
Until then though, the Trijet certainly ruled the roost in terms of regional airliners, but its true heyday was only just about to begin. By 1972, there were six major Trijet designs in operation across the globe; the pioneering Trident and Boeing 727, the Douglas DC-10, the Lockheed Tristar, the Tupolev Tu-134 and Tu-154. Of particular note in the lineup was the DC-10 and the L-1011, both of which were among the first long-range Trijets as well as incorporating a widebody design. This was comparable to only a handful of quad-jets (Boeing 707, Boeing 747, Vickers VC10 and Ilyushin Il-62) and an only slightly larger number of twinjets (Airbus A300, Boeing 737, Douglas DC-9, BAC 1-11, Sud Aviation Caravelle and Fokker F.28).
The advent of the Boeing 747, the world’s largest commercial airliner and an icon of American engineering, set the precedent for future long-range aircraft design. The narrow-body Boeing 707 and Douglas DC-8 were now so out of style they were practically medieval, thus the competition had to adapt to survive. All of the designs used for the American wide-body jet airliner spawned from different tenders handed out by the United States Air Force for a large transport aircraft. Douglas, Boeing and Lockheed all put their names into the hat with Lockheed coming out on top; contracted to build the now famous Lockheed C-5 Galaxy. However, the research and development gathered to create their military transport concepts gave Boeing and Douglas, as well as Lockheed, the impetus to follow through with a wide-body passenger airliner.
Boeing won the wide-body race in 1970 with the 747, a quad-jet, double-deck design which took the world by storm, finding its way into the hearts of airlines across the globe.
Douglas came second in 1971 with the DC-10, the world’s first long-range Trijet and one which defied convention in terms of the tail engine configuration. Rather than following the previous designs of the Trident and 727 by adopting an S-Duct, Douglas instead simply mounted a turbojet engine through the vertical stabiliser. Furthermore, for additional range, the aircraft placed large turbofan jet engines underneath the wings as their huge cross-sectional area meant they couldn’t be mounted to the fuselage itself.
Finally, in 1972, came the troubled Lockheed Tristar, arguably the better of the two Trijets but plagued with problems. The Tristar was the first Lockheed passenger airliner since the L-188 Electra turboprop of 1957, meaning they were quite a way behind in terms of both brand recognition and civilian aircraft design. This was coupled to the fact that the primary engine builder, Rolls-Royce, declared bankruptcy in 1971 while developing the RB-211 turbojet for the Tristar. It wouldn’t be until after the UK government had nationalised the company, split it from its luxury car division and reorganised the entire firm that engine production would finally regain its footing. However, the troubled nature of Rolls-Royce made the Tristar an unattractive buy, thus it was already in hot water to begin with.
Not like the DC-10 was any better.
In a bid to try and get their aircraft onto the market as soon as possible, Douglas had hurried the final stages of the development, resulting in a series of horrendous faults which came to bear throughout the early 1970’s. Most notably, the hinges and locks which secured the main cargo doors in place didn’t fit the fuselage properly, meaning that after constant pressurisation and depressurisation in their day-to-day operations they would become weak and have a propensity to fail.
This fault came to bear on June 12th, 1972, when American Airlines Flight 96 suffered an explosive decompression when the aft cargo door detached mid-flight. It was found that the door, which would not shut properly, had been forced shut by the ground crew. While this gave the impression of the door being shut, the locking mechanism hadn’t engaged properly, resulting in its failure. This early incident, which should’ve been heeded by the aviation industry and manufacturers, was largely ignored, being put down to improper maintenance and preparation rather than a fault with the aircraft’s design.
However, disaster truly struck on March 3rd, 1974, when Turkish Airlines Flight 981 crashed shortly after departure from Paris-Orly when, again, the cargo door detached mid-flight. The aircraft lost all hydraulic pressure and crashed into a forest near the town of Ermenonville. The results were the deaths of all 346 people aboard; making it the worst aviation incident until the Tenerife Disaster of 1977.
While an airworthiness directive was issued to see all DC-10’s undergo mandatory door modifications, the design of Trijets as a whole was brought into question. Following a slew of further fatal crashes involving the DC-10 throughout the decade, the general consensus soon became that the Trijet design was the primary fault with these aircraft, thus sales for the DC-10 dropped away as the 1980’s began.
As for the Tristar, the failure to launch the aircraft in time with the DC-10, the bankruptcy of Rolls-Royce and a later bribery scandal by Lockheed to try and get the L-1011 sold in Japan left the aircraft’s sales in tatters. The aircraft, which was highly advanced, reliable, safe, efficient and comparatively quiet, slipped silently off the production line in 1984, with only 250 units sold.
However, while one may consider Trijets more a victim of circumstance rather than a poor design option, the biggest problem of them all, one which undermined the Trijet concept as a whole, was about to be unleashed upon the world; Airbus.
In 1972, Airbus, a European multinational formed by governments of the European Union, unveiled the world’s first long-range twin-jet, the A300. The A300 combined the cutting edge of aviation technology with highly efficient but extremely powerful turbofan engines mounted below the wings, giving it equal range and performance to the likes of the 747 and the DC-10. Furthermore, it was wide-body, making it comparable in terms of capacity to the DC-10 and Tristar.
At first, the A300 was laughed off as an insolent upstart, but soon orders came in thick and fast. Perhaps the biggest blow to the American built Trijets was when in 1977, Eastern Airlines, one of the USA’s largest and most influential carriers, bought up several A300’s for use on their long-haul network. The A300 was also endearing in that it removed the Flight Engineer, with an early version of the Glass-Cockpit and computer aided design requiring only the need for two members of the flight crew. While the idea of ditching the Flight Engineer threw airline unions into a frenzy, it was a vision of the future and aircraft manufacturers, namely Boeing, incorporated the A300’s innovative elements into their own fleet of twin-jets; the Boeing 757 and 767.
The Boeing 757 and 767 were Boeing’s answer to the A300, efficiency and performance, but with no loss to the capacity. Both aircraft filled respective slots in the aviation market, the 757 being a narrow-body designed to replace ageing Boeing 727’s on short-to-medium haul runs, while the 767 would take on the A300 itself as a wide-body twinjet design.
The advent of these efficient twinjets, coupled with the disastrous fuel crisis of the 1970’s, meant that these aircraft were truly the future of aircraft design. While the Boeing 747 had the highest capacity and range of them all, unmatched until the late 1990’s, the A300, 757 and 767 was able to whittle away what little market the Trijets had left.
The 1980’s were truly the Trijet’s darkest hour; the Boeing 727 ended production in 1984 following the launch of the 757 and the L-1011, as mentioned, was withdrawn the same year with no replacement. The DC-10 soldiered on alone until 1989, though by the time production ended its sales had been reduced to a dribble, the only variants selling being freighters and the military KC-10. However, McDonnell Douglas, successor to Douglas, were not through with the Trijet idea yet, and gave the design one last stab in 1990 with truly the most advanced Trijet of them all; the McDonnell Douglas MD-11.
The MD-11 was designed as a last ditch attempt to show that twinjet alternatives had neither the range or the power to carry large payloads over large distances. The aircraft encompassed all the latest design features, including a glass-cockpit, highly efficient but extremely powerful engines, a huge fuselage cross-section which made it ideal for both passengers and freight, and could outfly pretty much every twinjet on the market.
When the MD-11 was launched in 1990, the only competition was the Boeing 767 and the A300. The Trijet could easily fly both further and faster than the two, it’s 7,200nmi range being 1,900 more than the A300, and nearly 4,000 more than the 767. It could also carry more passengers, with the MD-11 sporting a full capacity of 293 against the A300’s 266 and the 767’s 261.
However, while the MD-11 was something of a marginal success in its early years, being a beloved purchase of many important airlines, the nearly 30 year old design paled in comparison to an absolute myriad of twinjet options which were quickly deposited on its doorstep. First came the Airbus A330 twinjet and A340 quad-jet, both of which had higher range, higher efficiency and higher capacity; quickly stunting the MD-11’s sales run. Boeing responded by creating Extended Range (ER) versions of its 767, which could easily outperform the MD-11 on nearly all fronts and sold like hotcakes.
However, the biggest nail in the coffin of both the MD-11 and the Trijet legacy was 1995’s Boeing 777; the world’s first large-scale, long-range twinjet. The Boeing 777 could not only outperform and carry more passengers than the MD-11, it was comparable to the Boeing 747 as well in terms of its fantastic design. It was simple, easy and straightforward, but could deliver efficiency and size never before seen in a twinjet.
The result was the MD-11’s sales being utterly butchered, ending both the Trijet as a passenger airliner and McDonnell Douglas. The severe losses incurred in developing the MD-11, even with their highly successful MD-80 fleet still selling strongly, resulted in the manufacturer being bought by longtime rivals Boeing in 1997. Boeing continued to sell the MD-11 as a cargo aircraft until 2000, when, after a production run of 12 years and 200 units, the company decided to remove the issue of internal competition by discontinuing the MD-11, bringing the Trijet to a close.
While Trijets continued to be produced in Russia in the form of the Tu-134 and Tu-154, they only ever sold in the former states of the Soviet Union and its allies, and most designs, which dated back nearly 40 years, were discontinued shortly after the end of the Cold War in 1991.
The only other successful Trijet design were a few private jet models, including the Dassault Falcon 900. These models, while comparatively expensive, put speed and aerodynamic performance over the efficiency of twinjet models, with the highly successful Dassault Falcon 7X being one of only a handful of Trijets being produced for the mass market.
Today, Trijets are very difficult to find on a regular basis, especially in passenger service. In the face of more efficient and modern replacements, early Trijets such as the Trident, the 727, the DC-10 and the L-1011 were already on their way out by the time the new millennium came around. The fallout of September 11th and the crippling rise in fuel prices against falling profits was a major component in seeing most Trijet models retired by most large carriers by 2005. The final passenger use of Trijets under a major airline came down to the MD-11, which was retired by KLM in November 2014.
The 2000’s and 2010’s saw aircraft graveyards such as Mojave and Roswell become littered with redundant Trijets awaiting scrapping, the site of tail-mounted engines lining the horizon as far as the eye could see. Even today, many aircraft graveyards still have Trijets rusting quietly under the scorching sun.
Some Trijets have seen renewed life in the employ of cargo airlines, with MD-11’s and DC-10’s being prime movers for the likes of Fedex, UPS and Lufthansa Cargo. As for Boeing 727’s, their sheer numbers have seen many units still in operation across the world, mostly as freighters in developing countries. As for the Trident and the Tristar, their somewhat specialist nature saw them face early retirement and they have disappeared into obscurity.
So, the Trijet, what really did kill it and could it have been sustained?
Simply put; no.
The Trijet, while innovative at the time, could not have been sustained. It was, essentially, a stop-gap which covered the failings of early twinjets before better turbofan engines with increased reliability and range could be developed. While beautiful in design and being comparable to the quad-jets they locked horns with, it was a pervading thought that the twinjet would eventually reach a point that would see it outperform the Trijets and lead to their demise. Couple that with the fuel crisis, the catastrophic safety record of the DC-10, the inability of the L-1011 to sell and the MD-11 being an 8-track design in a CD-ROM world, and you have a recipe for disaster.
There was always a sense of inevitability to the end of the Trijets, but at least they did provide us with some of the most handsome and well performing aircraft of yesteryear. They are truly staples of their time, the concept of a three-engined jet airliner being very much an antique one, while twinjets are very much the here and now.
You just have to show someone an image of a DC-10, a Tristar or an MD-11, and they’ll immediately reminisce about the 1970’s and 80’s, when airport runways roared to the should of three-engined turbofan power!