The Hawker Siddeley HS121 Trident
When airlines crossed the decade line between the 1950s and 1960s, an increasing number of their long-range, high-capacity aircraft were powered by pure-jet engines, whose speed, comfort, and high-altitude characteristics resulted in overwhelming passenger acceptance. This soon prompted the question of whether this powerplant type would only serve this segment, as originally envisioned, or whether it would find its way on to lower-capacity, shorter-range aircraft once thought only appropriate for propeller technology.
BEA British European Airways was one of the first carriers to believe that it would. Although it ordered 20 Vickers Vanguards in December of 1956, a short-range airliner powered by four Rolls Royce Tyne turboprops and accommodating up to 139 single-class, six-abreast passengers, it foresaw the need for a few jet aircraft that could carry a similar number of passengers, but offer considerably higher cruise speeds. Seeking to fill this early-jet need and succeed its quad-engine Comet, de Havilland proposed the DH.121.
After the Hawker Siddeley Group was formed and the type became one of its projects, it was redesignated “HS.121” and its three-engine configuration earned it the “Trident” name.
The Hawker Siddeley HS.121 Trident, with a 114.9-foot span, a 35-degree sweepback, and a 1,358-square-foot area. featured a semi-monocoque fuselage constructed of both aluminum and copper alloy, and it was divided into a main, forward, pressured section, which ran as far as the side turbofan mounting positions, and an aft, unpressurized one, which supported the engines themselves, along with the vertical and horizontal tail. The nose and main gear wheel wells were also unpressurized, as was the wing center section.
The wings, whose span totaled 89.10 feet, were made of aluminum alloy stringers and skins and consisted of single, continuous wingtip-to-wingtip construction. They integrally contained a six-cell center section box across the fuselage, a two-cell box running from each wing root to a position equaling 40 percent of their span, and a single-cell box from this location to the tips. Each airfoil contained a drooped leading edge, three-section double-slotted trailing edge flaps, and alerions, all of which were of metal construction. Each forward outer flap additionally acted as an airbrake and each forward, inner one also served as a spoiler or lift dumper.
Leading and trialing edge devices, along with the ailerons, operated off of three independent hydraulic systems, only one of which was required for full activation, although there was no provision for manual reversion.
The all-metal tailplane, which featured a bullet fairing at the t-configured meeting point, was comprised of an all-moving horizontal stabilizer and a trialing edge geared, slotted, trim tab-devoid flap, and a rudder-provisioned vertical surface.
The tailplane gave the aircraft a 27-foot overall height.
Power was provided by three 9,850 thrust-pound Rolls Royce RB.163-1 Mk 525-5 low bypass ratio Spey turbofans, two of which were encased in aerodynamic nacelles and aft fuselage side-mounted, and one of which, with a triangular air intake, was installed in the tail and received its air feed by means of an above-fuselage intake that led to the exhaust cone by means of an s-duct path. Only the two fuselage-mounted engines were thrust reverser equipped.
The hydraulically actuated, tricycle undercarriage, deviating from what had become standard on commercial airliners, consisted of a twin-wheel nose gear that was mounted two feet to the left of the centerline so that forward baggage compartment space could be increased. It retracted laterally, to the right, and was provisioned with a Lockheed oleo-pneumatic shock absorber. The two quad-wheel main bogies, each featuring two tandemly arranged wheels, were provisioned with Hawker Siddeley shock absorbers. They uniquely rotated 90 degrees and increased in length by six inches during retraction and then settled into under-fuselage center section wells.
All nose and main gear units were equipped with Dunlop wheels and tires, multi-plate disc brakes, and Maxaret antiskid.
Fuel was stored in five wing-integral tanks, two of which were located in each wing and the fifth of which was installed in the fuselage center section.
Aircraft entrance was provided by three main, upward-opening, plug-type doors, the first of which was installed on the forward, left side, directly behind the flight deck, and used for passenger boarding; the second of which was installed on the mid-left side, immediately ahead of the wing leading edge; and the third of which was installed on the forward, right side. The latter two were used for galley provisioning. There were also two overwing emergency exits.
The Trident’, which was standardly flown by a three-person cockpit crew, featured an automatic landing system, which itself was operated by three independent autopilots. It was the first commercial airliner so-equipped and resulted from BEA’s requirements for an all-weather, year-round capable jet for operation on its European route network on which below-minimum conditions were frequently encountered.
The aircraft also featured, as previously mentioned, three independent hydraulic systems, each of which operated off of an engine-driven pump and powered the nose wheel steering, the brakes, the undercarriage, and all flight surfaces. Hydraulic system backup was achieved by means of two electrically-driven pumps.
A later-installed AiResearch GTCP-850 auxiliary power unit (APU), provided power for cabin conditioning, engine starting, and generator driving, the latter of which supplied electric power.
The passenger cabin was standardly configured with a forward, port lavatory and a starboard galley aligned with its servicing door and was usually followed by the first class section, which was in a four-abreast, two-two, arrangement. The mid, port galley door served as the natural separation between sections, the coach one usually in a six-abreast, three-three, arrangement. Two further lavatories were located in the tail.
Each reclining seat was equipped with a pull-down tray table, a literature pocket, an astray, and a seatbelt. Overhead passenger service units (PSU’s) featured fresh air vents, reading lights, and flight attendant call buttons. A single overhead rack, suitable only for coat, hat, pillow, and blanket storage, was installed on either side of the cabin. Sidewalls, interspersed by pull-down, shade-provided, oval windows, were molded.
Configuration, density, seat fabric and pattern, and carpet and galley/lavatory wall and door color varied according to customer request. An all-first class, four-abreast, two-two configuration, for instance, could have been chosen. Although BEA selected an 88-passenger, dual-class density, the aircraft’s maximum passenger capacity was 103. Any or all seats could be optionally installed in the rear-facing direction.
Lavatory water and toilet flushing worked off of a pneumatic system.
Cabin pressurization and air conditioning were attained by means of two Hawker Siddeley Dynamics air conditioning systems, only one of which was needed for complete cabin pressurization.
Baggage, cargo, and mail were carried in two below-deck holds located ahead of and behind the wing and accessed by a single starboard hatch. An air conditioning system could be optionally installed in the forward one to facilitate the transport of live animals.
Carrying a 22,000-pound payload, the Trident had a maximum takeoff weight of 115,000 pounds. Range, with this payload, was 930 miles and high cruise speed was 599 mph.
A comparison between it and its identically configured Boeing 727 counterpart serves to highlight their differences. Powered by the same number of turbofans, which were of a significantly lower thrust rating, the initial Trident 1 version accommodated 28 fewer passengers and offered a third less range, placing it more in a Caravelle III class, which was a twin-engine design.
FIRST FLIGHT AND SERVICE ENTRY
August 4, 1961 proved a milestone for BEA. Coincident with the delivery of the last of its 14 ordered Comet 4Bs was the rollout, from the Hatfield factory of its first Trident 1, draped in its livery and registered G-ARPA, although it was only fitted with two Spey engines at the time.
Appearing radically different than its predecessor, quad-engine counterparts that included the DH.106, the 707, and the DC-8, the Hawker Siddeley HS.121 Trident became the world’s first t-tailed tri-jet and technically de Havilland’s 121st design.
Seemingly shadowed by its US 727 equivalent during its subsequent sales tour, the Trident became the perpetual loser when it came to launch orders. In both Australia, one of the UK’s crown colonies, Hawker Siddeley was almost assured of sales, but ultimately failed to garner any, and in Japan, where both tri-jets were demonstrated to All-Nippon Airways and Japan Air Lines, the Boeing design once again won all the orders, leaving the Trident to return with nothing more than BEA’s 24-unit order and the thousands of fruitless miles it had covered.
While a blizzard delayed its targeted December first flight, it succeeded in achieving it on January 9, 1962. Under the command of de Havilland Chief Test Pilot John Cunningham, the 90,000-pound, t-tailed airliner took to the sky at a 130-knot speed, using only half of the 6,000-foot runway., The successful one-hour, 20-minute sorties, conducted as high as 15,000 feet and as fast as 330 knots, only experienced a single glitch when the starboard main gear became stuck during a retraction-extension test. Depressurization of one of the hydraulic systems remedied the situation.
After touchdown and a 3,000-foot deceleration on the runway, Cunningham commented, “I am delighted with the Trident’s handling qualities. She is superb to fly.”
The three-aircraft flight test program conducted by G-ARPA, -ARPB, and -ARPC, revealed two significant aerodynamic anomalies: the outboard ailerons were not necessary and a root-installed, moveable leading edge flap needed to operate in conjunction with the existing droop, both of which would improve the type’s lift at low speeds. G-ARPC was the first to fly without the outboard aileron.
Two other aircraft later joined the flight test program: G-ARPD, which first flew on January 17, 1963, tested the new leading edge high lift devices intended for an export version, and G-ARPE, which first flew six months later, on June 3, sported the first full-airline interior.
By December 12, aircraft G-ARPE undertook route-proving flights to 16 airports in 11 countries from London-Heathrow after its 80 airborne-hour demonstration tour to the Far East. BEA’s first aircraft, G-ARPF, was delivered at Stansted on December 12 for crew training and its Certificate of Airworthiness was granted two months later, on February 18, 1964, after a 1,600-hour flight test program.
Sporting an 80-passenger, dual-class interior, with a forward and mid galley, two aft-facing rows in the forward cabin, and three in the aft one, BEA’s Trident 1, G-ARPC, inaugurated Comet 4B substitution service on March 11 between London and Copenhagen, followed by additional and ad hoc flights to Geneva and Nice. But scheduled service officially commenced on April 1 to Zurich.
Ultimately operating its European route sectors and sometimes replacing its now outdated, turboprop-powered Viscounts, the type attracted ten-percent higher load factors.
A year after it had entered service, its 14 Tridents had carried more than 322,000 passengers and flown almost 3.7 million miles.
On April 1, 1965, it inaugurated “QuickSilver” air shuttle service between London and Paris with up to 13 weekday fights with the type, and in the summer, it operated the Amsterdam, Brussels, Copenhagen, Dusseldorf, Paris, and Zurich routes from Manchester, replacing Viscounts.
Demonstrating its capability, aircraft G-ARPR made the first commercial Autoland landing at London-Heathrow after its cross-channel sector from Paris-Le Bourget on June 10, 1965.
With its aerodynamically clean wings and aft-mounted turbofans, passengers enjoyed the type’s quiet, above-the-weather cruise on BEA”s short- to medium-range route network and it experienced high dispatch reliability amid some of the most adverse weather conditions because of its avionics and automatic landing capability.
Twenty-four Trident 1s were built, but their operation by a single carrier alerted of the fact that improvements to the basic design could attract additional sales, resulting in the Trident 1E.
THE TRIDENT 1C AND 1E
Seeking to improve the performance of the baseline Trident 1, Hawker Siddeley introduced a 1,000-Imperial gallon fuel capacity increase, resulting in the 1C version. All of BEA’s 24 aircraft were subsequently converted to this standard.
Hardly the cure-all to the design’s passenger capacity and range deficiencies, Hawker Siddeley incorporated additional features into the 1E (for “Export”) variant in order to procure sales beyond the insular UK area. Incorporating a 5.2-foot wingspan increase, which gave it a new 95-foot span and, hence, additional fuel tankage, it featured greater lift be means of full-span leading edge slats, which themselves replaced the Trident 1’s and 1C’s droop, improving low-speed lift. Its resultant wing area became 1,446 square feet.
Coupled with the wingspan increase and the leading edge devices were 11,400 thrust-pound Rolls Royce RB.163-25 Mk 511-5 Spey turbofans.
Although the aircraft retained the same internal dimensions, its greater payload capability enabled 115 passengers in a single-class, high-density arrangement to be accommodated, which was still 16 fewer than the 727-100’s maximum capacity, but it required the installation of two additional overwing emergency exits. Hinged, inward-opening entry doors were replaced with upward-sliding ones, creating unobstructed passage, and an internal reconfiguration took single-class capacity to between 106 and 139, the latter equaling that of the Vickers Vanguard.
Both payload and gross weights respectively increased to 25,170 and 135,500 pounds, and a new high-speed cruise of 605 mph was possible.
Sporting launch customer Kuwait Airways’ livery, which had made a two-firm and a single optioned order, the Trident 1E, registered G-ASWU, first flew from Hatfield on November 2, 1964 and was granted its Certificate of Airworthiness one year later.
Iraqi Airways, which became the second customer for the type when it ordered three Trident 1Es two years previously, actually became its first operator when It inaugurated it into service between Baghdad and London no November 22, 1965, albeit on only twice-weekly frequencies. Registered YI-AEA, it constituted its first pure-jet airliner. With March 5 and May 13 deliveries of its other two, it was able to serve Middle Eastern regional routes and those to Europe with its three-Trident fleet.
Pakistan International, which had made a three-firm and two-optioned order on January 26, 1964, placed the type into service two years later, on April 1, serving cities such as Kuwait to the west from its Karachi home base and Dacca and Baghdad to the east with it, replacing Viscounts and, in some cases, quad-engine Boeing 720s.
Aside from the ten Trident 1Es produced, another five HS.121-1E-140s were ordered by Channel Airways, which configured them for 139 passengers at a 31-inch pitch, but required a seven-abreast forward cabin to achieve. They had slightly higher, 135,800-pound gross weights.
Taking delivery, in the event, of only two for operation on charter, inclusive tour, and scheduled services, it relinquished the other three to BKS Air Transport, which took delivery of two, and Air Ceylon, which received the remaining one.
Fifteen improved HS.121-1Es and -1E-140s were altogether built.
While the Trident was designed around BEA’s limitations, BEA was eventually restricted by them. Expansion, in the fall of 1964, to Eastern Mediterranean markets, which exceeded the range of its Comet 4Bs, necessitated an aircraft with at least a 2,000-mile range so that it could serve destinations such as Beirut and Tel Aviv. The remedy was the Trident 2E, for which it made a 15-firm and 10-optioned order on August 5, 1965.
THE TRIDENT 2E
Key to the longer-range Trident 2E, whose fuselage remained dimensionally unchanged, was its three 11,960 thrust-pound Rolls Royce RB.163 Mk 512 Spey turbofans, which featured a redesigned first compressor stage. Installation of low-drag Kuchemann wingtips extended the span to 98 feet and increased the area to 1,462 square feet. A 350-Imperial gallon fuel tank was installed in the all-flying horizontal stabilizer and a slimmer tailplane bullet was employed. The APU, originally restricted to ground-only operation, was now usable in flight.
The version, with a 143,500-pound gross weight, and a new, 6,400-Imperial gallon fuel capacity, had a 2,400-mile range.
Wearing BEA colors and registered G-AVFA, first Trident 2E made its three-hour, 30-minute maiden flight on July 27, 1967 and was certified the following year, on April 15, after a four-aircraft, 533-hour flight test program.
The aircraft was now standardly quipped with two very high frequency omnidirectional range and instrument landing systems (VOR-ILS’s); dual automatic direction finders (ADFs); very high frequency and high frequency radios, the latter with Sel-Cal; three radio altimeters; a transponder; and weather radar.
While passenger capacity had increased, no internal dimension changes had occurred, leaving cabin length, excluding the cockpit, as 67 feet, 1.5 inches, width at 11 feet, 3.5 inches, and height at six feet, 7.5 inches.
Standard configuration entailed a lavatory and a single-unit galley on the forward, port and starboard sides, respectively, followed by three rows of first class seats in a four-abreast, two-two, arrangement. As had occurred on the Trident 1, 1C, and 1E, the mid-cabin access doors provided the natural divider between classes. The six-abreast, three-three, configured coach cabin was followed by two tail-installed lavatories, resulting in a 91-passenger complement. BRA, however, operated its 2Es with single-class, 97-passenger interiors. Although the type’s maximum capacity was 132, up to 149 could be accommodated in a high-density arrangement, but required several seven-abreast rows.
The unique configuration gave carriers the option of a three-class interior, consisting of a four-abreast first class, a six-abreast business or coach, and a seven-abreast economy one. Because of the density, the Trident’s overall capacity had increased by a third, from its original 103 to its current 149, but did not sacrifice payload for range due to its increased wing lift and higher-thrust engines.
Below-deck baggage, cargo, and mail volume had equally not changed. Its two holds, with 2.11- by 4.0-foot forward and 2.8- by 2.11-foot aft hatches still respectively offered 490- and 270-cubic-foot volumes.
Weights, however, had changed. Its maximum payload and takeoff weights had respectively increased to 26,800 and 143,500 pounds. Range, with a 16.020-pound payload, escalated to 2,500 miles, the latter primarily achieved with a new fuel volume that facilitated nonstop London-Middle East routes. Economy and high cruise speeds respectively increased to 596 and 605 mph. Its maximum landing weight was 113,000 pounds.
Although BEA occasionally substituted the type for the Trident 1C, it was officially inaugurated into service on June 1, 1968 with initial schedules to Dublin, Madrid, Milan, and Stockholm, but it subsequently replaced its Comet 4Bs with the type to Moscow and Eastern Mediterranean destinations, featuring three cabin configurations: 16 first and 73 economy, 8 first and 85 economy, and 97 in a single-class density.
Numerically the most popular version, with a 50-aircraft production run, it was operated by BEA itself (15), Cyprus Airways (2), and CAAC (33), the communist Chinese carrier’s first short-range western airliner.
Although its sales were hardly impressive, the basic Trident design, hampered by downsizing and engine unavailability, had achieved a degree of engineering success in and of itself. Employing its original fuselage, a marginally increased wingspan due to its new Kuchemann tips, and only slightly uprated Rolls Royce Spey turbofans, it approached its original, Medway-powered parameters by offering greater field performance, accommodating a third more passengers, connecting cities over 2,000 miles apart, and enjoying high dispatch reliability because of its Category II Autoland capability.
But growing traffic on certain routes required additional seating, as demonstrated by the Boeing 727, whose original -100 variant accommodated 131, but its succeeding -200 took this figure to the 189-mark. In order to remain competitive, Hawker Siddeley once again had to offer a higher-capacity, stretched variant, which took form as the Trident 3.
THE TRIDENT 3 AND 3B
The Boeing 727, once the follower of the Trident, became its leader-and the catalyst to a higher-capacity version to meet growing traffic demand. Powered by uprated Pratt and Whitney JT8D turbofans, it introduced a fuselage stretch; a fourth main door, which was located behind the wing, as its existing third now was; and a capacity increase from the 727-100’s 131 maximum to the 727-200’s 189, placing it in an accommodation category equal to that of the 720, but with one less powerplant.
Hawker Siddeley responded with its own higher-capacity, stretched-fuselage counterpart, the Trident 3, but limited Spey engine capability posed a far greater challenge and necessitated a longer than anticipated development period in which to surmount it.
The new version featured a fuselage length of 119.11 feet and a new overall length of 131.2 feet. Height had also increased-in this case, to 28.3 feet. Beyond the dimensional change, the mid, starboard door was relocated to the aft, right side, positioned only inches from the engine, and the number of overwing emergency exits was reduced by half, to two.
While the wingspan remained the same 98 feet as that of the Trident 2E, its overall area increased to 1,498 square feet, resulting in a wing loading of 100.5 pounds per square foot. Increased low-speed lift was attained by means of an additional flap span, the trailing edge double-slotted flaps now offering a 291.9-square-foot area. Two 15.3-square-foot, all-metal spoilers were also installed.
Fuel capacity decreased to 5,620 Imperial gallons, but an additional 380-Imperial gallon wing center section tank could be optionally chosen. Pressure fueling was undertaken at a single point on either wing. Oil capacity was three Imperial gallons per engine.
The vertical fin had a total area of 202 square feet, with the rudder alone measuring 52.1 square feet. The horizontal fin area was 300 square feet.
Power was still provided by the three 11,960 thrust-pound Rolls Royce RB.163-25 Mk 512-5W Spey turbofans that were fitted to the previous, shorter-fuselage Trident 2E, but the thrust shortage was uniquely resolved with the installation of a 5,250 thrust-pound Rolls Royce RB.162-86 booster jet below the rudder and just above the number two engine. It was fed by two air intake ducts positioned in the vertical tail and its exhaust cone was located directly above that of the number two powerplant.
Used only during takeoff and initial climb, the booster jet enabled the aircraft to overcome its increased weight, yet maintain respectable field performance without requiring the retrofit of a new engine type. As a result, he Trident 3 became the world’s first three-and-a-half engine airliner.
The larger version featured a stronger undercarriage to cater to the increased weights. With a 29 X 8 nose wheel tire size, whose pressure was 124 psi, and a 36 X 10 main wheel tire size, whose pressure was 165-psi, it retained its unique configuration with its off-center, laterally-retracting nose unit and tandem-wheeled, 90-degree rotating main ones.
Beyond the engine and wing modifications, an advanced automatic landing system certified for Category IIIA landings was installed.
The interior volume increase-the first and, in the event, the only one over that of the baseline Trident 1 and 2 variants-resulted in a new overall length of 83.5 feet, excluding the flight deck, and a new height of 6.8 feet, although its width remained the same. Because of the dimensional change, configurations were more flexible. Single-unit galleys were installed on both the forward port and starboard sides.
In a 14-passenger arrangement, the first class section consisted of a single pair of left-side seats and three rows of four-abreast ones at a 38-inch pitch. A 122-passenger coach section, separated by a curtained divider was in the standard six-abreast, three-three, configuration. Aft, port and starboard positions in the tail accounted for both single-unit galleys and lavatories.
Higher capacities were achieved with single-class arrangements, totaling 152 passengers at a 30-inch pitch and 180 at a 28-inch pitch, although the latter required the removal of some galley and lavatory facilities and a seven-abreast arrangement in the center section. In order to meet exit-limited evacuation requirements, a fifth door had to be installed on the aft, left side.
Lower-deck cargo volume commensurately increased-in this case, to 633 cubic feet in the forward hold and to 477 cubic feet in the aft one.
Weights, not surprisingly, were higher, increasing to a 38,722-pound payload and a 150,000-pound takeoff one, the latter of which required an 8,900-foot runway. Range, with its maximum fuel uplift, reserve allocations, and a 28,200-pound payload, became 2,860 miles, but decreased to 1,785 with its full payload. Its speeds varied from a 601-mph maximum at 28,300 feet to a 533-mph cruise at between 29,000 and 33,000 feet. Its 128,500-pound maximum landing weight necessitated a 5,690-foot runway.
Registered G-AWYZ, the first Trident 3 first took to the sky on December 11, 1969 without its booster jet, but achieved this feat three months later with it on March 22, using this additional power during acceleration and initial climb-out.
The five-aircraft, 14-month, 700-hour flight test program resulted in certification on February 8, 1971. British European Airways, which made a 26-firm and 2-optioned order for the elongated version, placed it into ad hoc service on March 1 of that year between London-Heathrow and Paris-Orly, sporting a 14-first and 119-coach cabin, but it officially entered scheduled operations the following month, on April 1, to Paris and Lisbon.
When the version was certified for Category IIIA landings in May of 1972, BEA had the rest of its Trident 1C and 2E fleet upgraded to this standard. As its European workhorse, the type provided reliable service and was well-received by passengers.
Although it was initially envisioned as meeting demand increases on inter-United Kingdom and European sectors, such as those from London to Amsterdam and Paris, its increased capacity failed to attract non-UK-carrier orders from the likes of Air France, Lufthansa, Iberia, Alitalia, and Olympic, which acquired the competing 727-200 instead.
A Trident 3B restored some of the larger-capacity version’s lost range, which increased to 1,900 miles, and was achieved with the installation of the 400-Imperial gallon center section fuel tank. Only two conforming to this standard, which had a 159,900-pound gross weight, were built for CAAC, leaving Hawker Siddeley with no option but to discontinue the program.
The Hawker Siddeley HS.121 Trident was the first three-engine jetliner and, because of the need to provide additional power for its first and only stretched version with a small, vertical tail installed booster jet, the first and only three-and-a-half one. De Havilland and later, Hawker Siddeley, succeeded in creating the design solution for an uneven number of powerplants by placing all three aft, but two were fuselage-mounted and the third was installed in the tail and fed by means of an s-shaped duct. Its t-tail configuration eliminated horizontal stabilizer exhaust interference and greater lift was generated with uninterrupted, aerodynamically clean, swept-back wings.
It represented the transition between the once conventional, intermediate-range, quad-engine Convair 880 and Boeing 720 designs and its own, introducing capacity and range variations in ratio to powerplant number, and became the first in a series of similarly-configured tri-jets that included the Boeing 727 in the US and the Tupolev Tu-154 and the Yakovlev Yak-42 in the USSR.
Although its early and innovative status should theoretically have guaranteed its success, its problem- and delay-plague program placed it at a disadvantage, entailing its initial design by one aircraft manufacturer, de Havilland, and its continued one by another, Hawker Siddeley; its application for a single customer, British European Airways, and not the world market; its downsizing and use of lower-rated turbofans that restricted its later growth and ability to meet other carrier needs; the time these obstacles lost, giving other manufacturers the opportunity to play catch-up and offer their own designs in what began as a virgin market, particularly that 727 in the US and the Caravelle in France, as airlines, responding to unprecedented passenger demand, realized that pure-jet technology was appropriate for all route sector lengths and that piston and turboprop aircraft would be quickly replaced by it.
Lastly, the political interferences that twice prompted British aircraft industry consolidation dealt the final attention deviating blow to a program that should have been solely about building airplanes.
Comparative sales of the two western tri-jets serve to prove the relative success of the Trident, which tackled these problems, and the 727, which did not, to each other. The former totaled 117 and the latter 1,832.
Nevertheless, the type’s innovative design configuration and its dual-fuselage length, seven-variant program, comprising the Trident 1, 1C, 1E, 1E-140, 2E, 3, and 3B, in which Hawker Siddeley poured every possible, rectifying feature into an aircraft plagued by inadequate power without employing a new engine type, emphasized its continual attempt to restore what it should always have been as the originally-sized and -engined de Havilland DH.121 and thus should hardly be discounted.