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One of the first trijets was the Boeing 727 airliner. A similar one to this was intentionally crashed for a television program.

A trijet is a jet aircraft powered by three jet engines. In general, passenger airline trijets are considered to be second-generation jet airliners, due to their innovative engine locations, in addition to the advancement of turbofan technology. Trijets are more efficient than quadjets, but not as efficient as twinjets, which replaced trijets as larger and more reliable turbofan engines became available.

Types still in production

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The Dassault Falcon 7X/8X and the Dassault Falcon 900 are the only civilian trijets in production and the Chengdu J-36 is the only military trijet in production.[citation needed]

Design

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Dassault Falcon 900EX. The 900 and its derivatives, the Falcon 7x and 8x, are the only trijets in production.

One consideration with trijets is positioning the central engine. This is usually accomplished by placing the engine along the centerline, but still poses difficulties. The most common configuration is having the central engine located in the rear fuselage and supplied with air by an S-shaped duct; this is used on the Hawker Siddeley Trident, Boeing 727, Tupolev Tu-154, Lockheed L-1011 TriStar, and, more recently, the Dassault Falcon 7X. The S-duct has low drag, and since the third engine is mounted closer to the centerline, the aircraft will normally be easy to handle in the event of an engine failure. However, S-duct designs are more complex and costlier, particularly for an airliner. Furthermore, the central engine bay would require structural changes in the event of a major re-engining (remodeling of the engine). For example, the 727's central bay was only wide enough to fit a low-bypass turbofan and not the newer high-bypass turbofans which were quieter and more powerful. Boeing decided that a redesign was too expensive and ended its production instead of pursuing further development. The Lockheed Tristar's tail section was too short to fit an existing two-spool engine as it was designed only to accommodate the new three-spool Rolls-Royce RB211 engine, and delays in the RB211's development, in turn, pushed back the TriStar's entry into service which affected sales.[1]

"Straight-through" central engine layout on the DC-10-based KC-10

The McDonnell Douglas DC-10 and related MD-11 use an alternative "straight-through" central engine layout, which allows for easier installation, modification, and access. It also has the additional benefit of being much easier to re-engine. However, this sacrifices aerodynamics compared to the S-duct. Also, as the engine is located much higher up than the wing-mounted engines, engine failure will produce a greater pitching moment, making it more difficult to control.

Manufacturer's model of the NR-349 improved manned interceptor proposal

The placement of the remaining two engines varies. Most smaller aircraft, such as the Hawker Siddeley Trident and the Boeing 727, as well as the intermediate-sized Tupolev Tu-154, have two side-mount engine pylons in a T-tail configuration. The larger widebody Lockheed TriStar and DC-10/MD-11 mount an engine underneath each wing. Preliminary studies were done on the TriStar to reuse the fuselage and wing for a twinjet design though these never materialized due to Lockheed's lack of funds. Additionally in the late-1990s Boeing, which had taken over McDonnell Douglas, considered removing the tail engine from the MD-11 to make it a twinjet but instead cancelled MD-11 production altogether.[1]

Advantages and drawbacks

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Trijets are more efficient and cheaper than four-engine aircraft, as the engines are the most expensive part of the plane and having more engines consumes more fuel, particularly if quadjets and trijets share engines of similar power. For widebody aircraft this makes the trijet configuration more suited to a mid-size airliner compared to the quadjet layout for jumbo jets (i.e. the DC-10 versus the quadjet Boeing 747). However the difficulty and complexity of mounting the third engine through the tail will somewhat negate the cost/efficiency advantage. Nonetheless, this was worth the trade-off in the 1960s to the 1990s when widebody trijets and twinjets shared engines of similar output, such as when the DC-10, MD-11, Boeing's 767, and Airbus's A300, A310, and A330 were all powered by the General Electric CF6, and the additional power from the third engine gave the DC-10/MD-11 advantages in longer range and/or heavier payload over the A300/A310/A330 twinjet. Since the 1990s, with further advancements in high-bypass turbofan technology, large twinjets have been equipped with purpose-designed engines such as the Boeing 777's General Electric GE90, allowing twinjets to perform the same tasks as most trijets and even many quadjets but more efficiently.

Due to their added thrust, trijets will have slightly improved takeoff performance compared to twinjets if an engine fails. Because takeoff performance for aircraft is usually calculated to include an extra margin to account for a possible engine failure, trijets are better able to take off from hot and high airports or those where terrain clearance near the runway is an issue.

The McDonnell Douglas MD-11 is the most recent airliner-size trijet produced.

Unlike twinjets, trijets are not required to land immediately at the nearest suitable airport if one engine fails. (This advantage is also shared with quadjets.)[2] This is advantageous if the aircraft is not near one of the operator's maintenance bases, as the pilots may then continue the flight and land at an airport where it is more suitable to perform repairs. Additionally, for trijets on the ground with one engine inoperative, approval can be granted to perform two-engine ferry flights. Prior to the introduction of ETOPS, only trijets and quadjets were able to perform long international flights over areas without any diversion airports. However, this advantage has largely disappeared in recent years as ETOPS-certified twin-engined aircraft are able to do so as well.

Another major advantage of the trijet design is that the wings can be located further aft on the fuselage, compared to twinjets and quadjets with all wing-mounted engines, allowing main cabin exit and entry doors to be more centrally located for quicker boarding and deplaning, ensuring shorter turnaround times. The rear-mounted engine and wings shift the aircraft's center of gravity rearwards, improving fuel efficiency, although this will also make the plane slightly less stable and more complex to handle during takeoff and landing. (The McDonnell Douglas DC-9 twinjet and its derivatives, whose engines are mounted on pylons near the rear empennage, have similar advantages/disadvantages of the trijet design, such as the wings located further aft and a more rearward center of gravity.)[citation needed]

History

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The Martin XB-51 was one of the first trijet designs.

The first trijet design to fly was the Tupolev Tu-73 bomber prototype, first flown in 1947.[3] The first commercial trijets were the Hawker Siddeley Trident (1962) and the Boeing 727 (1963). Both were compromises to meet airline requirements; in the case of the Trident, it was to meet BEA's changing needs, while the 727 had to be acceptable for three different airlines. Although collaboration between the manufacturers was considered, it did not come about.[4]

Early American twinjet designs were limited by the FAA's 60-minute rule, whereby the flight path of twin-engine jetliners was restricted to within 60 minutes' flying time from a suitable airport, in case of engine failure. In 1964, this rule was lifted for trijet designs, as they had a greater safety margin.

For second-generation jet airliners, with the innovations of the high-bypass turbofan for greater efficiency and reduced noise, and the wide-body (twin-aisle) for greater passenger/cargo capacity, the trijet design was seen as the optimal configuration for the medium wide-body jet airliner, sitting in terms of size, range, and cost between quadjets (four-engine aircraft) and twinjets, and this led to a flurry of trijet designs. The four-engine Boeing 747 was popular for transoceanic flights due to its long-range and large size, but it was expensive and not all routes were able to fill its seating capacity, while the original models of the Airbus A300 twinjet were limited to short- to medium-range distances. During this period, different jet airliners shared engines of similar output, such as when the McDonnell Douglas DC-10, Airbus A300, and Boeing 767 were powered by the General Electric CF6, the additional power from the third engine gave the DC-10 advantages in longer range and/or heavier payload over the A300 and 767 twinjets. Thus trijet designs such as the DC-10 and L-1011 TriStar represented the best compromise with medium- to long-range and medium size that US airlines sought for their domestic and transatlantic routes. As a result of these trijet wide-bodies, as well as the popularity of the Boeing 727, in their heyday of the 1980s trijets made up a majority of all such US jet airliners.

From 1985 to 2003 the number of such planes in service had sunk from 1488 to 602. The number of twinjets, on the other hand, had more than quadrupled in the same period.[5] Both Lockheed and McDonnell Douglas were financially weakened competing in the widebody market, which led to Lockheed ending production of the L-1011 in 1984 after producing only half the units needed to break even, while a number of fatal DC-10 crashes also slowed its sales.[1] In 1984 Boeing ended production of the 727, as its central engine bay would require an extremely expensive redesign to accommodate quieter high-bypass turbofans, and it was soon supplanted by Airbus with their A320 and Boeing with their 737 and 757. Further advancements in high-bypass turbofan technology and subsequent relaxation in airline safety rules made the trijet and even the quadjet nearly obsolete for passenger services, as their range and payload could be covered more efficiently with large twinjets powered with purpose-designed engines such as the 777's General Electric GE90.

During the 1980s, McDonnell Douglas was the only Western manufacturer to continue development of the trijet design with an update to the DC-10, the MD-11, which initially held a range and payload advantage over its closest medium wide-body competitors which were twinjets, the in-production Boeing 767 and upcoming Airbus A330. McDonnell Douglas had planned a new trijet called the MD-XX, which were lengthened versions of the MD-11. The MD-XX Long Range aircraft would have been capable of traveling distances up to 8,320 nautical miles (15,410 km) and had a wingspan of 65 metres (213 ft). The project was canceled in 1996, one year before McDonnell Douglas was acquired by Boeing. Boeing ended production of the MD-11 after filling remaining customer orders since the MD-11 would have competed with the 767 and 777. A study to remove the MD-11's tail-mounted engine (which would have made it a twinjet) never came to fruition as it would have been very expensive, and the MD-11 had very little in common in terms of design or type rating with other Boeing airliners.[6] In contrast to McDonnell Douglas sticking with their existing trijet configuration, Airbus (which never produced a trijet aircraft) and Boeing worked on new widebody twinjet designs that would become the A330 and 777, respectively. The MD-11's long-range advantage was brief as it soon was threatened by the A330's four-engine derivative, the A340, and the 777. The only other notable trijet development during the 1980s was in the Soviet Union, where the Tupolev Tu-154 was re-engined with the Soloviev D-30 engine as well as a new wing design and entered serial production from 1984 as the Tu-154M.

With the exceptions of the Dassault Falcon 7X, Falcon 8x, and Falcon 900 business jets, no manufacturer currently produces three-engine airliners.

Current status

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A Yakovlev Yak-40 on final approach

Modern engines have extremely low failure rates and can generate much higher shaft power and thrust than early types. This makes twinjets more suitable than they were before for long-haul trans-oceanic operations, resulting in eased ETOPS restrictions; modern wide-body twin-engine jets usually have an ETOPS 180 or (in the case of the Boeing 777 and 787) ETOPS 330 rating, and even ETOPS 370 for the Airbus A350.[7] As such, having more than two engines is no longer considered necessary, except for very large or heavy aircraft such as the Boeing 747, Airbus A380 (over 400 seats in a mixed-class configuration), Antonov An-124, and An-225, or for flights through the Southern Hemisphere, primarily to and from Australia (which has not yet adopted the ETOPS 330 standard), where the most direct route for some flights is over Antarctica.[8]

Since 2000, both narrow-body and wide-body trijet production has ceased for almost all commercial aircraft, being replaced by twinjets. As of 2016, the Falcon 7X, 8X, and 900 business jets, all of which use S-ducts, are the only trijets in production. Trijets that are no longer in production, such as the 727, Tu-154, DC-10, and MD-11, have found second careers as cargo aircraft, as well as in limited charter, governmental, and military service. However, because of the average age of trijets and the COVID-19 pandemic, most non-private operators have chosen to retire quadjets and trijets and replace them with more efficient and cost-saving twinjets. Today, the only widely used trijet is the MD-11, mostly operated by UPS Airlines and FedEx Express in cargo service.

For smaller private and corporate operators, where maximum fuel efficiency is often less important than for scheduled-route operating airlines, trijets may still be of interest due to their immunity from ETOPS and the ability to take off from shorter runways and therefore have access to more airports. As a result, a sizeable number of trijets, such as the newly built Dassault Falcons, are in use by private operators and corporate flight departments.

Future of trijets

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Airbus filed a patent in 2008 for a new, twin-tail trijet design, whose tail engine appears to use a "straight" layout similar to the MD-11, but it is unknown if and when this will be developed or produced.[9] However, the proposed Boeing X-48 blended wing body design, Lockheed's N+2 design study, and Aerion AS2 supersonic business jet were also supposed to have three engines.[10][11] The AS2 programme was cancelled in May 2021 when Aerion Corporation shut down.[12][13]

Boom Technology's planned Overture supersonic transport (SST) airliner was originally planned to use three engines, with the third engine installed in the tail with a Y-shaped duct and air intakes on both sides of the rear. However, a revised design with four engines located under a delta wing was unveiled at the Farnborough Airshow on July 19, 2022.[14]

On 26 December 2024, a trijet aircraft believed to be a Chengdu J-36 was spotted reportedly conducting test flights in Chengdu, Sichuan, China. Since the aircraft's serial number (36011) begins with '36,' following the People's Liberation Army Air Force convention, this model was presumably designated as J-36, but further information is limited.[15]

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Trijet

View on Grokipedia
from Grokipedia
A trijet is a jet aircraft powered by three jet engines, often configured either with two engines mounted under the wings and a third in the tail section or all three at the rear fuselage for enhanced thrust and balance during takeoff and climb. The first trijet was the British de Havilland DH.121 Trident, which had its maiden flight in 1962. Trijets emerged as a significant innovation in commercial aviation during the mid-20th century, bridging the gap between early quad-engine airliners and the later dominance of twin-engine designs. The configuration offered improved efficiency over four-engine aircraft for medium- to long-haul routes while providing the redundancy needed for extended overwater flights before advancements in engine reliability. Notable examples include the Boeing 727, the first American trijet with its first flight in 1963 and entry into service in 1964, which featured a rear-mounted triple-engine setup with a T-tail and became one of the best-selling commercial airliners with 1,832 units produced for short- to medium-range operations. Other prominent models were the McDonnell Douglas DC-10, a widebody trijet that entered service in 1971 (initial -10 variant with a maximum takeoff weight of about 430,000 pounds and range of 3,500 nautical miles; later variants up to 590,000 pounds and 6,500 nautical miles), and the Lockheed L-1011 TriStar, which made its maiden flight in 1970 and began commercial operations in 1972, incorporating advanced avionics and a center-tail engine. The popularity of trijets peaked from the to the , driven by their quieter cabins, faster passenger boarding via centralized doors in some designs, and superior performance at high-altitude or hot airports. However, by the 2000s, trijets largely faded from production as twin-engine aircraft like the and gained favor through the introduction of Extended-range Twin-engine Operational Performance Standards (ETOPS) regulations in the , which certified twins for long overwater routes with lower fuel consumption and maintenance costs. High operating expenses and the evolution of more powerful, efficient engines further accelerated their obsolescence, leaving only a handful of models, such as the business-oriented series, in limited use as of 2025.

Design and Configuration

Engine Arrangements

The primary engine arrangement in trijet features two engines mounted under the wings and a third in the rear , positioned tail-mounted to balance and enhance overall stability. This configuration emerged as a practical solution for medium- to long-range operations, providing the necessary for safe overwater flights during an era when regulatory restrictions limited twin-engine to routes within of a suitable . By incorporating three engines, trijets were certified for extended overwater operations under multi-engine rules without the added weight, drag, and maintenance complexity of four-engine designs, which were common on larger widebody jets of the time. Trijet central engine placements typically employ either a straight-duct or intake system to route airflow efficiently while minimizing aerodynamic penalties. In straight-duct designs, such as those on the and MD-11, the center is mounted at the base of the , with a linear intake pathway that draws air from the lower aft section, allowing straightforward airflow and easier scalability for higher-thrust engines or fuselage extensions. This arrangement positions the engine higher relative to the , reducing exposure to ground debris but requiring careful design to manage potential ingestion of fuselage air. Conversely, configurations, used in aircraft like the and , feature a curved, serpentine duct that draws air from the top of the , curving downward to feed the buried within the aft structure. The helps avoid ingestion of and low-energy fuselage flows by sourcing cleaner, higher-altitude air, though it introduces complexity and slight pressure losses due to the bends. Specific examples illustrate the performance benefits of these arrangements. The 727's central engine, powered by a , contributed to exceptional short-field capabilities, enabling operations on runways as short as 4,500 feet even under hot-and-high conditions, thanks to the combined of approximately 13,600 to 17,400 pounds per engine and the duct's role in optimizing airflow for rapid acceleration. In the DC-10, the straight-duct setup facilitated reliable for high-altitude takeoffs from airports like or , with the tail-mounted engine providing critical additional power while maintaining a simpler exhaust path that supported growth variants. These designs prioritized and distribution, allowing trijets to operate versatile routes in the 1960s and 1970s before advancements in twin-engine reliability diminished their necessity. Intake and exhaust systems in trijets incorporate unique adaptations for the central engine, including integration with units (APUs) and specialized reverser mechanisms. The APU, often located in the tail cone adjacent to the central engine compartment, supplies for starting all three engines and provides ground electrical power, with ducting arranged to avoid interference with the main intake pathways— for instance, in the L-1011, the APU's exhaust is routed separately to prevent contamination of the airflow. reversers on the central engine mirror those on wing-mounted units, typically employing clamshell or target-type mechanisms that redirect up to 50% of exhaust forward for deceleration; however, their fuselage-embedded position necessitates hydraulic or pneumatic actuation systems designed for limited access, ensuring symmetric reversal across all engines to maintain directional control during . These features enhance operational and efficiency, particularly on contaminated runways, by providing balanced braking without excessive reliance on wheel brakes.

Aerodynamic and Structural Features

The placement of the third engine in the tail of a trijet shifts the overall center of gravity rearward compared to equivalent configurations, requiring careful management through forward cargo or fuel loading to maintain longitudinal balance during flight and ground operations. This aft shift influences positioning, with the nose gear placed further forward to achieve optimal load distribution and propeller or jet clearance, as exemplified in the design where the gear arrangement supports the aft-biased weight while ensuring static stability on the ground. The integration of a central tail-mounted engine in trijets minimizes aerodynamic interference between the nacelles and the main wing, potentially reducing induced drag from pylon-wing interactions, but it introduces additional fuselage drag due to the complex S-duct intake required for air supply. Noise considerations are significant, as the tail engine's exhaust contributes to jet noise propagation; mitigation strategies include the use of vortex generators on control surfaces to manage airflow separation and boundary layer effects. These features help trijets meet certification noise limits, though the central engine's position can amplify perceived community noise compared to wing-mounted alternatives. Structural adaptations for the tail engine necessitate fuselage modifications, including reinforced bulkheads at the engine attachment points and robust pylon structures to distribute loads from the reverser and vibration damping systems. These reinforcements, often integrated with the , impose weight penalties from additional ducting and mounting hardware, primarily due to the need for strengthened aft bulkheads and load paths. Trijet configurations enhance directional stability, particularly in engine-out scenarios, by leveraging the centerline tail engine to counteract asymmetric thrust from wing engine failure, retaining approximately 67% of total thrust and reducing the yawing moment arm compared to twins (where only 50% thrust remains). The tail engine's thrust line is typically canted slightly upward to align with the aircraft's center of gravity, minimizing pitch excursions during power changes, while hydraulic actuators on the rudder provide augmented yaw control authority to maintain coordinated flight and prevent sideslip buildup. This setup allows for a more compact vertical tail surface, optimizing overall stability without excessive drag penalties.

Historical Development

Origins and Early Prototypes

The three-engine configuration for aircraft traces its roots to the piston-engine era of the 1920s, when trimotors like the Ford Trimotor were developed to enhance reliability and safety on early commercial routes, featuring a central engine supplemented by two wing-mounted units for redundancy. This design addressed the limitations of single- and twin-engine planes in an age of rudimentary aviation infrastructure, carrying passengers and mail across challenging terrains. As jet propulsion emerged post-World War II, the need for extended transatlantic range drove experimentation with multi-engine jet concepts, evolving from these early trimotors to meet demands for speed and endurance over oceans where diversion options were scarce. In the early 1950s, regulatory pressures from the U.S. Federal Aviation Administration (FAA) further propelled trijet exploration, as rules under the Civil Air Regulations—later codified in FAR Part 121—restricted twin-engine aircraft to operations within approximately 60 minutes' flying time of a suitable airport for extended overwater flights, due to engine reliability concerns. These requirements, rooted in 1950s safety standards and amended through the late 1950s to accommodate jet technology, made trijets (with three engines) preferable for longer routes, as they were exempt from the 60-minute limit and provided additional redundancy. The de Havilland Comet, the world's first commercial jet airliner with its 1949 prototype flight, indirectly influenced this shift by demonstrating jet viability but also underscoring multi-engine redundancy after its 1954 crashes highlighted operational vulnerabilities over remote areas. Key early developments included de Havilland's DH.121 proposal in 1957 for (BEA), leading to the after de Havilland's acquisition by in 1960; the Trident prototype first flew on January 9, 1962. Boeing's concurrent initiation of trijet transport studies in late 1959 focused on a rear-engine layout to improve short-field performance and access to regional airports while benefiting from the relaxed overwater rules for three-engine designs. This led to the creation of mockups by 1960 and culminated in the 727 prototype's first flight on February 9, 1963. Concurrently, European efforts like Sud Aviation's 1951 X-210 proposal for the SE-210 Caravelle envisioned a trijet with three turbojets—two in rear nacelles and one integrated into the fuselage—to achieve medium-haul range of over 2,000 km with 55-65 passengers. However, by 1953, advances in engines enabled a switch to a more efficient twin-engine configuration, abandoning the trijet amid shifting priorities for quieter cabins and lower operating costs. Several early trijet initiatives faltered due to market and technical challenges. For instance, while and persisted toward certification, other proposals like potential variants of existing designs struggled against the rising dominance of efficient twins and quads, highlighting the transitional nature of trijet concepts before widespread adoption in the mid-1960s.

Major Production Models

The , originally the DH.121, was the first commercial trijet airliner, with its prototype first flying on January 9, 1962, and entering service with BEA on April 1, 1964. This was designed for short- to medium-haul routes, accommodating 101 to 180 passengers depending on configuration, and featured rear-mounted engines with a for efficient operations at smaller airports. Key variants included the initial Trident 1 series and stretched models like the Trident 2 and 3, introduced in the late with improved range and capacity; a total of 117 units were built between 1962 and 1978. The debuted in service with in February 1964 following its on February 9, 1963. This was designed for short- to medium-haul routes, accommodating 149 to 189 passengers depending on configuration, and featured rear-mounted engines that enhanced short (STOL) capabilities suitable for smaller airports. Key variants included the original 727-100 and the stretched 727-200, introduced in 1967 with extended range for transcontinental operations; a total of 1,832 units were built between 1963 and 1984, making it one of the most prolific trijets in . In the , the emerged as an early regional trijet for short-haul routes, with its first flight on October 21, 1966, and entry into service with on September 30, 1968. This seated 27 to 32 passengers and was tailored for operations on unpaved runways common in the region, powered by three turbofans in a configuration with two rear fuselage-mounted engines and one in the tail; a total of 1,011 were produced from 1967 to 1981. McDonnell Douglas followed with the wide-body DC-10, which made its first flight on August 29, 1970, and entered service in 1971, capable of carrying 250 to 380 passengers on medium- to long-haul flights. The DC-10's trijet configuration, with engines under the wings and one in the tail, provided redundancy and efficiency for transoceanic routes; production totaled 446 aircraft from 1970 to 1989. Its successor, the MD-11, debuted with a first flight on January 10, 1990, and entered service later that year with , offering improved range for up to 410 passengers or dedicated freighter roles with strengthened floors and cargo doors. McDonnell Douglas produced 200 MD-11s between 1990 and 2000, many adapted for freight to extend their utility beyond passenger service. Lockheed's L-1011 TriStar, another wide-body trijet, achieved its first flight on November 16, 1970, and began operations in 1972 with , designed for 250 passengers on long-haul routes with advanced features like automatic landing systems. Powered exclusively by three high-bypass engines, it emphasized fuel efficiency and sophisticated for all-weather operations; Lockheed built 250 units from 1970 to 1984. In the Soviet Union, the Yakovlev Yak-42 emerged as a regional trijet for short-haul routes, with its first flight on March 7, 1975, and entry into service with Aeroflot in December 1977. This narrow-body aircraft seated 100 to 120 passengers and was tailored for operations on unpaved runways common in the region, powered by three Ivchenko D-36 turbofans; a total of 187 were produced from 1977 to 2003. For the business aviation sector, Dassault's Falcon 900 series debuted with a first flight on September 21, 1984, entering service in 1986 as a long-range executive trijet derived from the Falcon 50, accommodating 12 to 19 passengers in a luxurious cabin. Variants such as the 900B (1991), 900EX (1999), and 900LX (2005) progressively extended range to over 4,500 nautical miles with updated and engines; more than 500 units of the series have been produced since 1984. Trijet production peaked during the amid booming air travel demand, with major models like the , , Yak-40, and DC-10 driving output that collectively exceeded 2,000 units globally by the decade's end, before declining as twin-engine efficiency standards evolved and trijet development ceased with the MD-11 in 2000.

Operational Characteristics

Performance Advantages

Trijets provided substantial advantages in operational range and route flexibility through their three-engine , which circumvented the stringent diversion time limits imposed on twin-engine before the evolution of ETOPS regulations. In the pre-1980s era, twinjets were generally restricted to flights within of an adequate , severely limiting their suitability for overwater or remote routes. Trijets, however, were exempt from the 60-minute diversion rule applicable to twinjets, allowing operations on extended transoceanic and remote routes and enabling airlines to serve long-haul international markets. For instance, the McDonnell Douglas DC-10-10 offered a range of about 3,500 nautical miles, sufficient for transatlantic segments such as New York to , compared to the early Boeing 737-100's limited 1,500 nautical miles, which confined it to shorter domestic routes. The additional thrust from the third engine also enhanced payload capacity, particularly for operations from challenging airports with short or high-altitude runways. This configuration allowed trijets to outperform early twinjets in carrying heavier loads without compromising takeoff performance. The Boeing 727 exemplified this capability, achieving payloads of up to 40,000 pounds on runways under 5,000 feet, which facilitated efficient cargo and passenger transport to secondary cities ill-equipped for larger aircraft. Safety was further bolstered by the trijet's , ensuring robust engine-out performance where the aircraft could maintain flight and climb with two operational . The rear-mounted center played a key role in mitigating asymmetric effects; upon failure of a wing , the centerline reduced the resulting yaw moment, requiring less deflection for control and easing under FAA standards for continued safe operation. This design simplified handling during critical phases like takeoff, where the aircraft retained adequate margins for obstacle clearance. Short-field operations represented another hallmark advantage, with trijets like the capable of takeoffs from runways as brief as 4,500 feet at , thanks to the combined and aerodynamic features optimized for low-speed . This versatility expanded jet service to over 100 regional airports worldwide, democratizing to areas previously reliant on propeller aircraft.

Economic and Maintenance Challenges

Trijets incurred higher acquisition costs due to the inclusion of a third , which increased complexity and material requirements compared to twin-engine designs. For instance, the carried a list price of approximately $20 million upon its entry into service in 1972, reflecting the premium for its advanced trijet configuration over simpler alternatives of the era. Operating expenses were similarly elevated, as the additional contributed to greater consumption and overall direct operating costs, making trijets less competitive against increasingly efficient as technology advanced in the 1980s and 1990s. Maintenance presented substantial challenges for trijet operators, primarily because the centrally mounted engine was embedded within the or tail structure, complicating access for routine inspections and overhauls. In the , for example, servicing the number-two engine often necessitated partial disassembly of the and surrounding components, leading to extended downtime and labor-intensive procedures that could exceed 100 hours for major checks. This lack of parts commonality across the three engines further exacerbated costs, as airlines had to maintain separate inventories and training for varied engine types, unlike the streamlined logistics of fleets. The rearward placement of engines in many trijets also amplified noise and emissions issues, with exhaust proximity to the cabin elevating interior sound levels. Measurements in the recorded cabin noise up to 84 dBA during cruise, significantly louder than contemporary twinjets and contributing to passenger discomfort. Fuel inefficiency translated to higher CO2 emissions per seat-mile, with trijets producing approximately 10-15% more than ETOPS-capable twinjets by the , as the third engine's drag and weight offset any redundancy benefits. Certification requirements under FAR Part 36 imposed additional hurdles, as evolving standards progressively restricted older trijets. Many models, such as unmodified 727s classified as 2 aircraft, faced phase-out mandates by the early 2000s unless retrofitted with costly hush kits to achieve 3 compliance, ultimately accelerating the retirement of these designs from commercial service.

Current Production and Fleet Status

Models Still in Production

As of 2025, the only trijet aircraft models remaining in active production are in the business jet segment, specifically the Dassault Falcon 900LX and Falcon 8X, both manufactured by Dassault Aviation in France. These executive jets represent a continuation of trijet designs tailored for long-range private and corporate operations, following the decline of commercial trijet airliners after the McDonnell Douglas MD-11's production ended in 2000. The Dassault Falcon 900LX, an upgraded variant of the Falcon 900 series introduced in 2010, remains in production for long-range business missions. Powered by three TFE731-60 engines each delivering 5,000 lbf (22.25 kN) of , it offers a maximum range of 4,750 nautical miles (8,800 km) and accommodates 12 to 16 passengers in a versatile cabin configuration. Approximately 100 units of the 900LX have been built since its launch, with recent deliveries including the first of three new aircraft to operator LUMINAIR in September 2025. Certified by both the (EASA) and the (FAA) for private operations, it features a (MTOW) of around 53,000 lb (24,040 kg). The Dassault Falcon 8X, entering service in 2016 as the flagship trijet model, continues production with enhancements over its Falcon 7X predecessor, including advanced fly-by-wire controls and improved aerodynamics. It is equipped with three Pratt & Whitney PW307D engines, each providing 6,722 lbf (29.90 kN) of thrust, enabling a range of 6,450 nautical miles (11,945 km) and capacity for 12 to 16 passengers. Over 100 units have been produced to date, with Dassault maintaining an annual output of approximately 10 Falcon 8X aircraft as part of its broader business jet production rate of about 40 units across models in 2025. Like the 900LX, it holds EASA and FAA certification, with an MTOW of 73,000 lb (33,113 kg). This focus on executive trijets reflects a post-2000 industry shift away from fuel-intensive commercial airliners toward efficient, specialized business , with all occurring at Dassault's facilities in Martignas-sur-Jaille and other sites in .

Active Operators and Usage

In 2025, commercial operations of trijet have become exceedingly rare, with no major airlines maintaining scheduled services using these models. The , once a staple for short- to medium-haul routes, saw its last regular flights in regions like and around 2019, driven by stringent noise regulations and the shift to more efficient twin-engine jets. Small regional carriers in and occasionally operate converted 727s for limited duties, but the global active fleet numbers fewer than 10 , all facing imminent phase-out due to aging airframes and regulatory pressures. Cargo and freighter conversions represent the primary domain for legacy trijets, particularly in short-haul and long-range express delivery. The McDonnell Douglas MD-11F remains the dominant model, with approximately 56 active worldwide prior to recent events, operated mainly by (29 units), , and for transcontinental freight routes. However, following a fatal UPS MD-11 crash on November 4, 2025, in , which prompted FAA-mandated inspections for potential structural issues, both and UPS grounded their entire MD-11 fleets on November 8, 2025, suspending operations temporarily while awaiting clearance. freighters, numbering around 22 globally, continue in niche roles, with Serve Air Cargo in the of Congo operating four for domestic in challenging environments. McDonnell Douglas DC-10 freighters and tankers, limited to fewer than 10 active units, serve specialized purposes such as by 10 Tanker Air Carrier and medical missions by Orbis International's Flying Eye Hospital; however, on November 17, 2025, the FAA expanded the grounding order to include all DC-10 and MD-10 variants pending inspections for similar structural concerns. Business and private aviation sustains the largest segment of active trijets, centered on Dassault Falcon models prized for their balance of range, speed, and reliability in transcontinental operations. The Falcon 7X leads with approximately 299 aircraft in service, followed by the Falcon 8X (108 units) and Falcon 900 series (around 118 units), totaling over 500 Falcon trijets worldwide, often managed by programs like . These aircraft achieve high utilization rates, averaging more than 400 flight hours per year, supporting executive travel on routes up to 6,450 nautical miles, such as New York to . Operators value the trijet configuration for its redundancy and performance in hot-and-high conditions, though maintenance costs remain a consideration for older 900 variants. The global trijet fleet stands at roughly 500 active aircraft in 2025, a sharp decline from a peak of over 2,500 in the , with about 80% retired or stored due to economic and environmental factors. Trijets maintain a strong safety profile, with major hull-loss incidents occurring at a rate of approximately one per million flights across models like the and , bolstered by redundant engine designs and rigorous certification standards. Usage trends indicate continued reliance on Falcons for premium private flights, while legacy cargo trijets like the MD-11 face accelerated retirements amid fleet groundings and the rise of twin-engine alternatives.

Future Prospects

Proposed and Canceled Concepts

McDonnell Douglas explored the MD-100 in the early 1980s as a proposed stretched trijet successor to the DC-10, retaining the three-engine layout to enhance range competitiveness with ETOPS-certified twins, targeting up to 7,500 nautical miles while accommodating more passengers; the proposal, initiated in 1981 to revive large trijet development, was canceled by November 1983 amid insufficient airline interest and shifting market preferences toward twinjets. During the 1970s, conducted studies for a three-engine widebody configuration as part of early A300 development, considering it to match competitors like the DC-10 but ultimately rejected the trijet approach in favor of a twin-engine design for better efficiency, lower operating costs, and differentiation in the market; this decision shaped the A300 as the first twin-engine widebody airliner. In the and later , the trijet received proposed upgrades in the 1990s through the Yak-42D variant, incorporating extended range via additional fuel tanks, improved , and enhanced performance for mid-range operations up to 120 seats; while some modernization efforts were implemented, broader upgrades including potential re-engining were shelved due to economic constraints and the rise of more efficient twinjets.

Potential for Revival

Advancements in hybrid-electric propulsion systems present a potential technological enabler for reviving trijet designs by improving the efficiency of a third engine, as and are developing megawatt-class hybrid-electric components that could integrate into future aircraft configurations to reduce fuel consumption by up to 20% compared to conventional engines. Although these efforts focus on single-aisle twinjets, the modular nature of the technology could adapt to trijet layouts for enhanced in long-haul operations. Additionally, sustainable aviation fuel (SAF) offers compatibility with existing trijet engines, such as those on the Dassault Falcon series, enabling up to 80% reductions in lifecycle without requiring aircraft modifications, as SAF is a for conventional . Market drivers for trijet revival include niches in ultra-long-range and cargo transport, where configurations like the Dassault Falcon 8X trijet provide ranges of 6,450 nautical miles, supporting nonstop flights such as New York to without refueling. In emerging markets with underdeveloped airport infrastructure, trijets could offer advantages over twins by bypassing strict ETOPS requirements for remote or oceanic routes, historically allowing operations up to 120 minutes from diversion airports without the need for extended twin-engine approvals. Significant challenges hinder trijet development, including the dominance of twinjets, which account for virtually all new long-haul orders due to their and operational flexibility. Regulatory advancements favoring twins, such as FAA approvals for up to 370 minutes of ETOPS on aircraft like the , enable them to fly nearly any global route, further marginalizing multi-engine designs. Moreover, clean-sheet aircraft programs, including potential trijet variants, face R&D and certification costs estimated at $10-15 billion, deterring investment amid the established Boeing-Airbus duopoly. As of 2025, no firm trijet projects have materialized, though ongoing battery technology advancements toward higher densities could enable hybrid-electric trijets by 2035, potentially addressing gaps if integrated with innovations. Industry analyses indicate that without substantial breakthroughs in , the economic barriers will likely prevent widespread revival, limiting trijets to specialized roles.

References

  1. https://eaglepubs.erau.edu/introductiontoaerospaceflightvehicles/chapter/history-of-aircraft-and-aviation/
  2. https://www.dot.mn.gov/aero/aviationeducation/documents/publications/historyaircaftdottodot.pdf
  3. https://simpleflying.com/mcdonnell-douglas-dc-10-variants-guide/
  4. https://www.boeing.com/history/products/lockheed-l-1011.page
  5. https://simpleflying.com/history-trijet-rear-engined-planes-demise/
  6. https://www.dassault-aviation.com/en/civil/falcon-family/falcon-900lx/
  7. https://simpleflying.com/why-mcdonnell-douglas-build-dc-10-3-engines/
  8. https://simpleflying.com/age-of-the-tri-jet/
  9. https://mondortiz.com/the-s-duct-intake-of-the-lockheed-tristar-and-boeing-727/
  10. https://simpleflying.com/why-boeing-build-727-3-engines/
  11. https://www.tristar500.net/library/designfeatures.pdf
  12. https://patents.google.com/patent/US3666211A/en
  13. https://ntrs.nasa.gov/api/citations/19970031272/downloads/19970031272.pdf
  14. https://ntrs.nasa.gov/api/citations/19750015496/downloads/19750015496.pdf
  15. https://ntrs.nasa.gov/api/citations/20050186546/downloads/20050186546.pdf
  16. https://doi.org/10.1016/j.trpro.2018.02.015
  17. https://ntrs.nasa.gov/api/citations/20200000513/downloads/20200000513.pdf
  18. https://www.faa.gov/sites/faa.gov/files/about/history/people/Ford_Trimotor.pdf
  19. https://www.boeing.com/content/dam/boeing/boeingdotcom/history/pdf/Boeing_Products.pdf
  20. https://www.thrustflight.com/etops/
  21. https://simpleflying.com/hawker-siddeley-trident-story/
  22. https://www.key.aero/article/developing-boeing-727
  23. https://hushkit.net/2022/05/26/10-reasons-the-sud-aviation-caravelle-jetliner-is-fantastic/
  24. https://avgeeks.aero/why-three-engines-the-rise-and-fall-of-tri-jet-aircraft/
  25. https://simpleflying.com/boeing-727-variants-guide/
  26. https://secure.boeingimages.com/archive/Rollout-for-the-First-727-2F3XC5QDBU1.html
  27. https://ig.space/commslink/boeing-727-groundbreaking-tri-jet-was-the-best-sel/
  28. https://simpleflying.com/yakovlev-yak-40-first-flight-anniversary/
  29. https://secure.boeingimages.com/archive/DC-10-Series-20-First-Flight-2F3XC58P3SW.html
  30. https://asn.flightsafety.org/database/types/McDonnell-Douglas-DC-10/specs
  31. https://airwaysmag.com/legacy-posts/american-dc-10-into-service
  32. https://www.airfleets.net/listing/md11-1.htm
  33. https://asn.flightsafety.org/database/types/McDonnell-Douglas-MD-11/specs
  34. https://www.faa.gov/about/history/timeline
  35. https://www.lockheedmartin.com/en-us/news/features/history/l-1011.html
  36. https://www.key.aero/article/yak-42-soviet-trijet-tribulations
  37. https://www.forecastinternational.com/archive/disp_old_pdf.cfm?ARC_ID=1055
  38. https://www.dassault-aviation.com/en/passion/aircraft/civil-dassault-aircraft/falcon-900/
  39. https://www.globalair.com/articles/the-most-popular-variants-of-the-dassault-falcon-900?id=7185
  40. https://simpleflying.com/etops-evolution-history/
  41. https://www.federalregister.gov/documents/2007/01/16/07-39/extended-operations-etops-of-multi-engine-airplanes
  42. https://simpleflying.com/boeing-737-early-model-development-history/
  43. https://planetags.com/blogs/planetags-blog/american-airlines-dc-10-the-jet-that-defined-a-generation-of-air-travel
  44. https://aerospaceweb.org/aircraft/jetliner/b727/
  45. https://www.boeing.com/content/dam/boeing/boeingdotcom/company/about_bca/startup/pdf/historical/727-100-20_passenger.pdf
  46. https://www.boeing.com/content/dam/boeing/boeingdotcom/company/about_bca/pdf/StartupBoeing_ETOPS.pdf
  47. https://jonbeckett.substack.com/p/the-boeing-727-200
  48. https://aerocorner.com/aircraft/lockheed-l-1011-tristar-1/
  49. https://www.eplaneai.com/news/why-trijets-are-no-longer-produced
  50. https://www.quora.com/Why-are-we-seeing-fewer-and-fewer-trijet-commercial-aircraft
  51. https://flyusa.com/private-jets-with-3-engines/
  52. https://pmc.ncbi.nlm.nih.gov/articles/PMC5777454/
  53. https://simpleflying.com/5-reasons-tri-jets-arent-made-anymore/
  54. https://www.faa.gov/air_traffic/noise_emissions/noise_levels
  55. https://www.dassaultfalcon.com/
  56. https://flycraft.com/basics/the-reason-for-three-engine-trijet-private-jets/
  57. https://www.eplaneai.com/news/why-the-aviation-industry-phased-out-tri-jet-commercial-aircraft
  58. https://www.dassaultfalcon.com/businessjets/falcon-900lx/
  59. https://www.aviationjeta.com/luminair-falcon-900lx-delivery/
  60. https://www.dassaultfalcon.com/businessjets/falcon-8x/
  61. https://www.avbuyer.com/aircraft/private-jets/dassault-falcon/8x
  62. https://www.dassault-aviation.com/en/
  63. https://simpleflying.com/how-many-boeing-727s-left/
  64. https://simpleflying.com/which-airlines-still-fly-trijets-today/
  65. https://www.facebook.com/Flight.everyday1/posts/%25EF%25B8%258F-the-md-11-refuses-to-die-the-tri-jet-that-still-rules-the-cargo-skies-more-tha/761489393610662/
  66. https://www.airwaysmag.com/new-post/major-cargo-operators-ground-md-11-fleets
  67. https://www.flightglobal.com/safety/us-faa-broadens-md-11-grounding-order-to-remaining-dc-10-fleets/165313.article
  68. https://www.avbuyer.com/aircraft/private-jets/dassault-falcon
  69. https://www.guardianjet.com/jet-aircraft-online-tools/aircraft-brochure.cfm?m=Dassault-Falcon-7X-98
  70. https://www.guardianjet.com/jet-aircraft-online-tools/aircraft-brochure.cfm?m=Dassault-Falcon-8X-194
  71. https://www.guardianjet.com/jet-aircraft-online-tools/aircraft-brochure.cfm?m=Dassault-Falcon-900EX-101
  72. https://www.airlinereporter.com/2014/10/the-end-of-the-passenger-widebody-trijet-saying-goodbye-to-the-md-11/
  73. https://www.airbus.com/en/newsroom/stories/2018-06-airbus-jetliners-a-standard-setting-history
  74. https://www.nasa.gov/aeronautics/nasa-ge-hybrid-electric-research-092024/
  75. https://afdc.energy.gov/fuels/sustainable-aviation-fuel
  76. https://magellanjets.com/aircraft/book-private-jet-dassault-falcon-8x/
  77. https://www.flyaeroguard.com/learning-center/etops-explained/
  78. https://www.ati.org.uk/wp-content/uploads/2021/08/insight_10-the-evolving-aerospace-rd-landscape.pdf
  79. https://simpleflying.com/aircraft-highest-etops/
  80. https://www.idtechex.com/en/research-report/advanced-li-ion-batteries-2025-2035-technologies-players-markets-forecasts/1087
  81. https://ntrs.nasa.gov/api/citations/20190033478/downloads/20190033478.pdf
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