From the 1960s and 1970s, three-engine trijet aircraft were a common sight with many airlines. They served an important role. Three engines were more economical than four, but flight operations were not limited as strictly as twin-engine aircraft. With the rise in twins’ ability and the introduction of ETOPS regulations, the popularity of trijets decreased. For a long time, though, they formed a significant part of many airline fleets – especially in the US and in Russia.
Introducing the trijet
The first jet aircraft flown commercially were four-engine quadjets. The de Havilland Comet was the first, with its four engines mounted within the wings. It suffered several problems, though, which limited its success. The Boeing 707 is often credited as the first truly successful jet and the start of the jet age for many airlines.
The 727 followed from Boeing as a smaller aircraft, capable of using smaller airports and runways. Other manufacturers launched trijets for longer haul operations. These worked well for many airlines. One less engine led to a reduction in operating costs. But they offered good performance and the ability to operate over water.
From the 1980s, though, trijets fell out of favor with many airlines. The main reason for this was the introduction of ETOPS regulations. From 1985, twin-engine aircraft were permitted to fly further from a diversion airport, extending the options to use them on transoceanic services. This started with a 120-minute rating, but 180 minutes soon became common. Today, ratings go up to 370 minutes for the A350. Trijets quickly lost their place, with the dominance of twin engines continuing today.
The Boeing 727
The Boeing 727 was by far the most sold and operated, trijet. It first flew in 1963 and remained in production up to 1984. Boring built 1,832 aircraft – vastly more than it originally intended.
The largest operators of the 727, just as with the 707, were in Boeing’s home market of the United States. Most of the major US airlines at the time operated the 727. Boeing designed the 727 for this market. It gave the ability to operate at smaller airports and had a flap system to support this.
Aircraft came and went at different times. The three largest airlines all operated significant fleets – United Airlines with 245 aircraft, Delta Air Lines with 201 aircraft and American Airlines with 184 aircraft. These figures are based on data obtained from AeroTransport Data Bank (
Also in the US, Eastern Air Lines operated 183 aircraft, Pan American 152 aircraft, Northwest Airlines 115 aircraft, and TWA 112 aircraft.
Outside the US, several European airlines also had large fleets. Lufthansa operated 63 aircraft, Iberia 56 aircraft, and Air France 30 aircraft. Japanese airlines ANA had a fleet of 47 727s,
Douglas soon followed Boeing with a new trijet. It launched the DC-10 in 1968, entering service in August 1971 with American Airlines. This was not really a competitor to Boeing and the 727. It was a long-haul aircraft introduced as a replacement for the four-engine DC-8. Douglas delivered 286 DC-10 aircraft to airlines. A further 60 were sold as tankers.
Again, the DC-10 was most popular in the US. American Airlines led the way with 68 aircraft, and United Airlines operated 59. Continental Airlines had 49 DC-10s and Northwest Airlines 48. The notable exception was Delta Air Lines, which went more with the L-1011, and Pan Am, which only operated 17 DC-10s and moved from the Boeing 707 to the 747. Notable fleets in Europe included KLM with 23 aircraft, Alitalia with 18 aircraft, Lufthansa with 17, and Iberia with 14.
Lockheed L-1011 TriStar
Lockheed introduced the L-1011 TriStar in 1970 to compete against Boeing and Douglas’ offerings. It went on to deliver 250 aircraft – somewhat less than it could have. It was a good aircraft, but coming to the market after the DC-10 cost it customers.
Delta Air Lines was the largest operator of the type, with a total of 71 aircraft. It was also the only airline to operate all the L-1011 variants. Eastern Air Lines and TWA also had large fleets, with 63 and 57 aircraft respectively. In Europe, British Airways operated a total of 29 L-1011s.
It was not just US manufacturers that launched trijets in the 1960s and 1970s. The USSR manufacturer Tupolev introduced the Tu-154 trijet in 1968. It entered service with Aeroflot in 1972. It offered similar specifications to the Boeing 727 and the Hawker Trident but served the Soviet market.
Aeroflot was by far the largest operator of the aircraft – and with it, the largest operator of any trijet. Over 1,000 Tu-154 aircraft were built, and Aerfolot operated over 700 of them over the years. It retired its last only in 2009.
Hawker Siddeley Trident
The Hawker Siddeley Trident was the British offering in the trijet market. It entered service in 1964, mainly competing with the Boeing 727.
Unsurprisingly, it did not feature in US airline fleets but was popular in the UK and Europe. Hawker delivered 117 aircraft, with the largest fleet operated by British European Airways (later to become part of British Airways), with up to 74 aircraft.
McDonnell Douglas MD-11
The McDonnell Douglas MD-11 is the most recent sizeable commercial trijet (there are others still in production in the small private/corporate jet market). It was developed as a successor to the Douglas DC-10 and entered service in 1990 with Finnair. 200 aircraft were delivered to airlines.
In passenger service, American Airlines has operated 25 aircraft, and Delta Air Lines’ 18 aircraft. It has, though, been more used in cargo service. FedEx Express and UPS Airlines both operate large fleets up to today.
Trijets have formed significant parts of many airlines fleets in the past. Several remain in service, but not many in passenger use. Many more airlines have operated them in the past – this has just been a look at some of the most significant. Feel free to discuss this long and varied history further in the comments.