Hawker Siddeley Trident

Background and original specification In 1953, as British European Airways (BEA) introduced the world's first turboprop-powered civil airliner – the Vickers Viscount – into passenger service, the operator was already considering what would be required of a potential successor. Following the entry into service of jet airliners in 1952, many airline managers and economists remained sceptical, and advocated turboprop airliners as replacements of piston-engined airliners. In 1953, while several manufacturers across the world were investing in pure jet-powered aircraft, BEA chose to favour turboprops on the basis of their superior economics and produced a specification that called for an aircraft capable of seating 100 passengers and attaining a maximum speed of . As a result of the BEA specification, Vickers developed an enlarged derivative of the Viscount for BEA, the Vickers Vanguard, which was ordered by the airline on 20 July 1956. By this point, however, the French-built Sud Aviation Caravelle had conducted its maiden flight during the previous year, and BEA was beginning to recognise that jet aircraft could soon be providing stiff competition. In April 1956, Anthony Milward, chief executive of BEA, stated that he "would rather do without [jet airliners]". Nevertheless, in December of that same year Lord Douglas of Kirtleside, BEA's chairman, stated that a number of jet-powered short haul aircraft might need to be introduced while retaining turboprop aircraft as the mainstay of the company's inventory for the foreseeable future. According to aviation author Derek Woods, BEA "wanted something that was faster than the Caravelle which was threatening to be highly competitive". While they were not intended as an express requirement, commentators ever since have taken these figures to constitute a definite call to industry. By August 1957, the DH.121 proposal had been revised; differences included the adoption of the in-development turbofan, the Rolls-Royce Medway, and an expansion to accommodate a maximum of 98 passengers. The design initially included a cruciform tail layout similar to that of the Caravelle. beneath the flight deck From the outset, the DH.121 was planned to employ avionics that were very advanced for the period. Among other capabilities, they would offer automatic approach and landing within a few years of service entry. The avionics were also to have triplicated components for reliability and to allow "majority 2:1 voting" for aircraft guidance during automatic approach and landing. The physical dimensions of most avionics of the period required them to be housed in a large compartment beneath the Trident's flight deck; the compartment's size was among the factors dictating a distinctive nose undercarriage design, with the nose landing gear offset by to the port side and retracting sideways to stow across the DH.121's longitudinal axis. Industry consolidation and selection BEA soon selected the DH.121 as the basis for detailed negotiations, but these talks were protracted due to multiple factors, including wider policy decisions of the British government and indecision within BEA itself. Companies vigorously competed to be selected by BEA due to the lure of its £30 million contract (), as well as the likelihood of lucrative overseas export sales. On 4 February 1958, de Havilland, along with Hunting and Fairey, announced that they had agreed to form a partnership for the purpose of manufacturing and marketing the DH.121; the consortium adopted the corporate name of the defunct Airco company, which had been Geoffrey de Havilland's employer during the First World War. Boeing had begun its studies into this sector of the market in 1956, and elected to launch its own trijet programme in 1959. Airco executives, who were at the time intensely exploring various alternatives and further partnerships with other aircraft companies, considered the possibility that Boeing might choose to drop the 727 project and instead co-manufacture the DH.121 in the USA; Lord Douglas was one of the proponents of this initiative. Woods remarked that "de Havilland solemnly handed all its research over to its rivals ... the crowning piece of stupidity". A further six months were needed for the government to approve a formal BEA order for the DH.121; the government had favoured the Bristol 200 for industrial policy reasons. Reportedly, BEA had a considerable interest in the Caravelle itself, but this would have been a politically unacceptable choice. BEA also favoured , and therefore the Trident submission, due to the firm's established experience with jet airliners with its prior development of the Comet. According to Woods, this enlarged version of the DH.121 was "on the verge of building the right aeroplane for the market and the success of the Viscount looked like being repeated". The airline's concerns reflected three factors - a short-lived airline recession in the late 1950s; the imminent arrival into service of a large fleet of turboprop Vickers Vanguards, which duplicated the DH.121's general payload-range area; and the growing trend to higher-density seating. Although de Havilland stated that they generally concurred with BEA, its management also stated that they had worked "under terms more onerous than anything D.H. had previously undertaken". Industry observers at the time felt that the British aircraft industry had again stumbled "into the pitfall of having designed exclusively for one customer an aeroplane that has potentially a much wider scope": Downsizing the Trident involved substantial changes to the design being made, including a powerplant change from the Medway to a scaled-down derivative, the 40% less powerful 9,850 lbf (43.8 kN) Rolls-Royce Spey 505. Woods summarised the BEA-mandated redesign as: "At one blow the 121 was emasculated in terms of size, power and range". It was this revised aircraft that BEA ultimately ordered on 24 August 1959, initially in 24 examples with 12 options. In September 1960, the future airliner's name, Trident, was announced at the Farnborough Airshow; this name had been chosen as a reflection of its then-unique three-jet, triple-hydraulic configuration. Further development and proposals By 1960, de Havilland had been acquired by the Hawker Siddeley group. After the de Havilland takeover, Airco was disbanded. Hunting was marshalled into the competing newly formed British Aircraft Corporation (BAC); their departure removed any putative possibility of the Hunting 107 (later the BAC One-Eleven) being marketed alongside the DH.121 as a complementary, smaller member of the same airliner family. Fairey Aviation, partially incorporated into Westland Aircraft, also left the DH.121 project. With the move to Hawker Siddeley Aviation, the designation was eventually revised to the HS 121. The reorganisation of the industry had compounded upon the delays caused by BEA's changes to the specification, which had in turn harmed the Trident's competitiveness against the Boeing 727. The rival Boeing 727 had quickly established a lead over the Trident. The 727's early lead only strengthened it in subsequent competitions; one such example is Trans Australia Airlines, which had determined the Trident to be superior to the Boeing 727 from an operational standpoint, but it was also viewed as having been commercially risky to choose a different fleet from rival airlines such as Ansett Australia, which had already selected the 727. In 1972, its unit cost was US$7.8M. By 1975, only 117 Tridents had been sold against over 1,000 727s. According to Woods, a significant opportunity that may have enabled the Trident to catch up with the 727 was lost during the 1960s in the form of two competitions for a maritime patrol aircraft; a NATO design competition to replace the Lockheed P-2 Neptune, and Air Staff Requirement 381, which sought a replacement for the Royal Air Force's piston-engined Avro Shackleton. In addition to the maritime patrol requirement, Avro envisioned that the aircraft could be used in various military roles, including as a 103-seat troop transport and as being armed with up to four GAM-87 Skybolt air-launched ballistic missiles as a nuclear-armed bomber. In addition to Avro's proposals, Armstrong Whitworth had also proposed their own military variants of the Trident. Rolls-Royce Limited, having shelved development of the Medway following the Trident's redesign, was keen to develop an engine to slot between the 10,000 lb Spey engine and the 20,000 lb Rolls-Royce Conway engine; if such an engine had been produced, it could have equipped new versions of the civil Trident, as well. Furnished with a more capable engine that could provide more thrust than the Spey could, an extended fuselage could also have been adopted and existing landing restrictions could have been discarded; overall, the Trident would have been a far closer match to the 727. Wood summarised the importance of this prospective development as: "For the Trident programme, the RB.177 would have been a God-send". At one point, the Avro 776 looked set to win the competition to be selected as the RAF's new maritime patrol aircraft. Due to a desire to cut costs, though, the RAF decided to issue an entirely new operational requirement, under which the demands for speed, endurance, and capacity had all been diminished. As a result of the changes, the design team was recalled and the Avro 776 was entirely sidelined for a new proposal. ==Design==

Overview The Trident was a jet airliner of all-metal construction with a T-tail and a low-mounted wing with a quarter-chord sweepback of 35 degrees. It had three rear-mounted engines: two in side-fuselage pods, and the third in the fuselage tailcone, with an S-shaped intake duct. One version, the 3B, had a fourth "boost" engine with a separate intake duct above the main S-duct. All versions were powered by versions of the Rolls-Royce Spey, while the boost engine was a Rolls-Royce RB162, originally intended as a lift engine for VTOL applications. The Trident was one of the fastest subsonic commercial airliners, cruising at over . At introduction into service its cruise Mach Number was 0.88/ 380 kn IAS. Designed for high speed, with a critical Mach number of 0.93, the wing produced relatively limited lift at lower speeds. This, and the aircraft's low thrust-to-weight ratio, called for prolonged takeoff runs. Nevertheless, the Trident fulfilled BEA's field length criterion and its relatively staid airfield performance was deemed adequate before the arrival into service of the Boeing 727 and later jet airliners built to field length criteria. The aerodynamics and wing was developed by a team led by Richard Clarkson, who would later use the Trident wing design as the basis for the wing of the Airbus A300; for the Trident he won the Mullard Award in 1969. The Trident normal descent rate was up to 4500 ft/min (23 m/s). In emergency descents of up to 10,000 ft/min, it was permissible to use reverse thrust. Below 280 kn IAS, it was also possible to extend the main landing gear for use as an airbrake. The Trident's first version, Trident 1C, had the unusual capability of using reverse thrust prior to touchdown. The throttles could be closed in the flare and reverse idle set to open the reverser buckets. At pilot discretion, up to full reverse thrust could then be used prior to touchdown. This was helpful to reduce hydroplaning and give very short landing runs on wet or slippery runways while preserving wheel brake efficiency and keeping wheel brake temperatures low. Brakes were fitted with the Dunlop Maxaret anti-skid system. Avionics on the centre instrument panel The Trident had a complex, sophisticated and comprehensive avionics fit which was successful in service. This comprised a completely automatic blind landing system developed by Hawker Siddeley and Smiths Aircraft Instruments. It was capable of guiding the aircraft automatically during airfield approach, flare, touchdown and even roll-out from the landing runway. The system was intended to offer autoland by 1970. In the event, it enabled the Trident to perform the first automatic landing by a civil airliner in scheduled passenger service on 10 June 1965 and the first genuinely "blind" landing in scheduled passenger service on 4 November 1966. The ability to land in fog solved a major problem at London Heathrow and other British airports. Delays were commonplace when Category 1 (Cat 1 = decision height and 600 metre runway visual range RVR) instrument landing system (ILS) was in use. The Trident's autoland system pioneered the use of lower landing minima, initially with Category 2 (100 ft decision height and 400 metres RVR) and soon after "zero-zero" (Category 3C) conditions. Since Tridents could operate safely to airfields equipped with suitable ILS installations, they could operate schedules regardless of weather, while other aircraft were forced to divert. Later the system included a voice recorder. ==Operational history==

Introduction The first Trident entered service on 1 April 1964. Trident 3B The Trident was becoming the backbone of BEA's fleet and BEA wanted an even larger aircraft. offered two new designs in 1965: a larger 158-seat two-engine aircraft otherwise similar to the Trident known as the HS132; and the 185-seat HS134, which moved the engines under the wings, a design very similar to the Boeing 737. Both were to be powered by a new high-bypass engine under development at the time, the Rolls-Royce RB178. BEA instead opted for Boeing 727s and 737s to fill the roles of both the BAC 1–11 and Trident, but this plan was vetoed by the British government. BEA returned to Hawker Siddeley and chose a stretched version of the basic Trident, the Trident 3. A fuselage stretch of made room for up to 180 passengers; raised the gross weight to and made modifications to the wing to increase its chord; the engines remained the same. BEA rejected the design as being unable to perform adequately in "hot and high" conditions, in light of such difficulties experienced with the Trident 2E. Since the Spey 512 was the last of the Spey line, extra thrust would be difficult to obtain. Instead of attempting to replace the three engines with a different type, which would have been difficult with one engine buried in the tail, 's engineers decided to add a fourth engine in the tail, the tiny Rolls-Royce RB162 turbojet, fed from its own intake behind a pair of movable doors. The engine added 15 per cent more thrust for takeoff, while adding only 5 per cent more weight, and it would only be used when needed. BEA accepted this design as the Trident 3B, and ordered 26. The first flight was on 11 December 1969 and the aircraft entered service on 1 April 1971. Addition of extra fuel capacity resulted in the Super Trident 3B. The Trident experienced some key export sales, particularly to China. Following a thawing of relations between Britain and the People's Republic of China, China completed several purchase deals and more than 35 Tridents were eventually sold. In 1977, fatigue cracks were discovered in the wings of British Airways Tridents. The aircraft were ferried back to the manufacturer and repaired, then returned to service. The beginning of the Trident's end came in the early 1980s, since ICAO began drafting noise regulations that would require first- and second-generation jet airliners to fit hush kits to the engines. These regulations would go into effect on 1 January 1986. British Airways, the type's main operator, saw the refits as not viable and instead chose to phase the Trident out of their fleet in 1985, the final flights were made on 31 December 1985. The Trident's services in China ended in 1995, marking its permanent retirement from service. Only 117 Tridents were produced and all are out of service. In contrast, 1,832 Boeing 727 aircraft (designed to the Trident's original specification) were built and the last continued in passenger service until 2019. ==Variants==

;Trident 1C: Production version for British European Airways; 24 built ;Trident 1E: Increased seating capacity, uprated engines, and addition of leading edge slats over the Trident 1C; 15 built ;Trident 2E: An improved Trident 1E with triplex autoland system; 50 built ;Trident 3B: High-capacity short-medium range version of the 2E with a stretch and one additional RB.162 booster engine (for take-off and climb) in the tail; 26 built ;Super Trident 3B: Extended range by 692 km (430 miles); two built ==Operators==

Trident 1E, March 1978 Trident 1E /British Airways livery. Civil operators ;Ceylon (now Sri Lanka) • Air Ceylon received one of the cancelled Channel Airlines Trident 1Es in 1969, and operated it until 1978. ;China • Air China operated 5 former CAAC Tridents from 1988 to 1991. • CAAC Airlines received 4 former PIA Trident 1Es in 1970, followed by 33 new Trident 2Es between 1972 and 1978, and a pair of Super Trident 3Bs in 1975. • China United Airlines operated former CAAC Tridents ;Cyprus • Cyprus Airways received two Trident 2Es in 1969/70, one of which was damaged in 1972 and swapped for a similar BEA aircraft. Two former Kuwait Airlines Trident 1Es were acquired via BEA in 1973. Two aircraft were damaged beyond repair during the Turkish Invasion of Cyprus in 1974, one of which was left on the abandoned Nicosia airport and remains. The two survivors passed to British Airways in 1977. ;Iraq • Iraqi Airways received three Trident 1Es in 1965, which were operated until 1977. ;Kuwait • Kuwait Airways received three Trident 1Es in 1965/66. One was written off in 1966 and the others were sold to BEA in 1972. ;Pakistan • Pakistan International Airlines received four Trident 1Es in 1966–67, including a VIP aircraft for presidential flights. They were sold to China in 1970. ;United Kingdom • BKS/Northeast Airlines received two of the cancelled Channel Airways Trident 1Es in 1969 and acquired a third example from Channel in 1971. One was written off in 1975 and the others passed to British Airways when Northeast was taken over in 1976. • British Airways inherited 20 Trident 1Cs, one Trident 1E, 15 Trident 2Es and 26 Trident 3Bs from British European Airways in 1974. Two more 1Es were added when Northeast Airlines was absorbed in 1976, and a 1E and a 2E (both one-time BEA machines) came from Cyprus Airways in 1977. BA retired its Trident fleet between 1974 and 1985. • British European Airways received 23 Trident 1Cs in 1964–66, a 24th aircraft having crashed on its test flight. These were followed by 15 Trident 2E (1968–70) and 26 Trident 3Bs (1971–73). A Trident 1E was acquired from Channel Airways in 1971. One of the 2Es was swapped for a damaged Cyprus Airlines example in 1972, while two former Kuwait Airlines 1Es were operated in 1972 before passing to Cyprus Airways in 1973. Three Trident 1Cs were written off whilst in BEA ownership and the rest of the fleet passed to British Airways upon its formation in 1974. • Channel Airways ordered five Trident 1Es but only two were delivered, in 1968. These were sold to BEA and Northeast Airways in 1971. ;Zaire • Air Charter Service of Zaire received five former British Airways Trident 3Bs in 1984–86. Military operators ;China • People's Liberation Army Air Force operated former CAAC Tridents ;Pakistan • Pakistan Air Force was the intended operator of the presidential Trident 1E, but it was delivered to Pakistan International Airways instead. ==Accidents and incidents==

Accidents with fatalities • On 3 June 1966, Trident 1C registration G-ARPY entered into a deep stall while on a test flight and crashed at Felthorpe, Norfolk, killing all four crew. • On 13 September 1971, a People's Liberation Army Air Force Trident 1E crashed in Mongolia under mysterious circumstances during an attempt by Lin Biao and his family to defect to the Soviet Union according to the official view of the PRC. Official PRC accounts claim that the Trident ran out of fuel, but others claim the plane was actually destroyed from controlled flight into terrain during radar evasion. • On 18 June 1972, British European Airways Flight 548, a Trident 1 registered G-ARPI, entered a deep stall due to pilot error and crashed at Staines shortly after takeoff from Heathrow Airport. All 118 on board were killed in what became known as the "Staines air disaster". , it is still the worst aviation accident to have occurred on British soil (accident, versus the Pan Am Flight 103 terrorist incident). • On 10 September 1976, British Airways Flight 476, a Trident 3B registered G-AWZT, collided in midair with Inex-Adria Aviopromet Flight 550 a McDonnell Douglas DC-9 registered YU-AJR, over Yugoslavia, killing everyone on both aircraft. The collision of the two aircraft was attributed to an air traffic control error. • On 14 March 1979, a CAAC Airlines Trident 2E registered B-274, crashed into a factory near Beijing, injuring at least 200. The crash was caused by an unqualified pilot who stole and flew the airliner. All 12 people on board were killed, as well as 32 people on the ground. • On 26 April 1982, a CAAC Trident 2E registration B-266, operating as CAAC Flight 3303, crashed near Yangsuo, China killing all 112 passengers and crew. • On 14 September 1983 a CAAC Airlines Trident 2E registered B-264 was hit by a military aircraft while on the runway at Guilin Airport, China. Eleven passengers were killed. • On 31 August 1988, the right outboard flap of a CAAC Trident 2B operating as CAAC Flight 301 hit approach lights of runway 31 of Hong Kong's Kai Tak Airport while landing in rain and fog. The right main landing gear struck the seawall of the reclaimed land on which the runway was laid and was torn out, causing the aircraft to run off the runway and slip into the harbour. Seven people were killed. Hull losses • On 30 June 1966, Kuwait Airways Trident 1E registration 9K-ACG crash-landed 3 miles short of the runway at Kuwait International Airport. Fortunately there were no fatalities, and only minor injuries amongst the 83 passengers & crew. The aircraft which was just over one year old was written off. • On 3 July 1968, whilst parked at Heathrow Terminal 1, Trident 1s G-ARPI and G-ARPT were struck by an Airspeed Ambassador G-AMAD operating BKS Air Transport Flight C.6845, which crashed whilst landing on runway 28R, thereafter departing from the runway. Trident G-ARPI was severely damaged, but repaired and returned to service, whereas G-ARPT was written off. G-ARPI later crashed in 1972. • On 15 September 1975 Trident 1E G-AVYD was damaged beyond repair & written off at Bilbao after aborting its take-off at or close to V1, and failing to stop on the remaining length of (wet) runway. It was operating British Airways (Northeast Airlines) flight NS552 with 110 passengers and 7 crew, all of whom evacuated the aircraft safely. Incidents • On 23 July 1974, a British Airways Trident suffered a bombing attempt while over the sea. It diverted to Manchester Airport. • On 5 May 1983, CAAC Flight 296 was hijacked, leading to establishment of diplomatic relations between the PRC and ROK. ==Aircraft on display==

, Beijing • Trident 1C G-ARPH (Nose Section) at Museum of Flight East Fortune Scotland. • Trident 1C G-ARPO at North East Land, Sea and Air Museums Sunderland, UK in Northeast Airlines (UK) livery. • Trident 1C G-ARPP (Nose Section) at Solway Aviation Museum Carlisle Airport UK. • Trident 1E B-2207 at Civil Aviation Museum, Beijing, China. • Trident 1E 50051 at Beijing Air And Space Museum. • Trident 2E 50055 at the Military Museum of the Chinese People's Revolution, Beijing, China. • Trident 2E 50057 at Zhuhai. • Trident 2E G-AVFB at Imperial War Museum Duxford, Duxford, Cambridgeshire, UK; on display in British European Airways livery. • Trident 2E G-AVFH (Forward Fuselage Section) at the De Havilland Museum Hertfordshire. • Trident 2E G-AVFM (Nose Section) at South Wales Aviation Museum St Athan Wales. • Trident 3B G-AWZI (Nose Section) at Farnborough Air Sciences Trust Museum. • Trident 3B G-AWZJ (Forward Fuselage Section) Dumfries and Galloway Aviation Museum. • Trident 3B G-AWZK at Runway Visitor Park at Manchester Airport, Manchester, UK; moved from Heathrow in September 2005 after fund raising campaign by The Trident Preservation Society and Neil Lomax on display in British European Airways livery. • Trident 3B G-AWZM at the Science Museum's National Collections Centre exhibit store at Wroughton, Wiltshire, UK; preserved in British Airways 'Negus' livery. • Trident 3B G-AWZP (Nose Section) at the De Havilland Museum Hertfordshire. • Trident 3B G-AWZU (Nose Section) at Jet Age Museum Gloucester. ==Specifications==