Hawker Siddeley Trident
|Trident 1 G-ARPC at the SBAC Farnborough Airshow, 8 September 1962.|
|Role||Narrow-body jet airliner|
|National origin||United Kingdom|
|First flight||9 January 1962|
|Introduction||1 April 1964|
|Primary users||British European Airways
The Hawker Siddeley HS 121 Trident (originally the de Havilland D.H.121 and the Airco DH 121) was a British short and medium-range airliner. It was the first T-tail rear-engined three-engined jet airliner to be designed. It was also the first airliner to make a blind landing in revenue service in 1965.
The Trident emerged in response to a call by the state-owned British European Airways Corporation (BEA) for a jet airliner for its premier West European routes. BEA had been induced by the government to issue this call despite its unwillingness to buy a large jet fleet. The airline's requirements fluctuated greatly in the 1950s and a decade later evolved radically away from what the Trident could offer. Adherence to BEA's changing specification was widely seen as limiting the Trident's appeal to other airlines and delaying its service entry.[N 1]
During its gestation, the Trident was also involved in a government drive to rationalise the British aircraft industry. The resulting corporate moves and government interventions contributed to delays causing it to enter service two months after its major competitor, the Boeing 727, losing further potential sales as a result.
By the end of the programme in 1978, 117 Tridents had been produced. BEA's successor British Airways withdrew its Tridents by the mid-1980s. Trident services ended in China in the early 1990s.
- 1 Development
- 2 Design
- 3 Operational history
- 4 Variants
- 5 Operators
- 6 Survivors
- 7 Accidents
- 8 Specifications
- 9 See also
- 10 References
- 11 Further reading
- 12 External links
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 April 1956, Anthony Milward, chief executive of British European Airways (BEA) stated that he "would rather do without [jet airliners]". Nevertheless, in July the same year, BEA announced what it called "outline requirements" for a short-haul "second generation jet airliner", to work alongside BEA's large fleet of turboprop airliners. It would carry a payload of some 20,000 lb (9,100 kg) or some 70 passengers over up to 1,000 miles (1,600 kilometres), weigh about 100,000 lb (45,000 kg), use 6,000 ft (1,800 m) runways, cruise at a very high speed of 610 to 620 mph (980 to 1,000 km/h) and have "more than two engines".[N 2] While not an express requirement, commentators ever since have taken these figures to constitute a definite call to industry.
Four companies prepared projects to match the BEA outline. Bristol proposed the initially-four-engined Bristol Type 200. Avro also proposed the rather futuristic Avro 740 trijet before shelving it and joining forces with Bristol and Hawker Siddeley. Vickers proposed the VC11 four-engined aircraft, derived from its VC10 then in development. The de Havilland company considered three possible contenders for the specification. Two were four-engined developments of the Comet: the D.H.119 and the D.H.120, the latter also intended for offer to British Overseas Airways Corporation (BOAC). The third, the D.H.121 announced in May 1957, had three engines and was pitched at BEA. In February 1958 BEA announced that the D.H.121 had come closest to its requirements and that it would order 24 with options on 12 more. It took a further six months for the British government to approve a formal BEA order for the D.H.121; the government had favoured the Bristol 200 for industrial policy reasons. Reportedly, BEA had a considerable interest in the French Sud Aviation Caravelle; this would have been a politically unacceptable choice, so BEA had to favour de Havilland and the Trident.
The D.H.121 was to be the world's first trijet airliner. Its designers felt this configuration offered a trade-off between cruising economy and take-off safety in case of an engine failure; moreover, the BEA specification had called for "more than two engines". Each of the three engines would drive its own hydraulic system, offering triple redundancy in case of any of the other systems failing. The engines were to be 13,790 lbf (61.34 kN) Rolls-Royce Medways. The D.H.121 was to have a gross weight of 123,000 lb (56,000 kg) or optionally, up to 150,000 pounds (68,000 kg), a range of 2,070 miles (3,330 kilometres), and seating for 111 in a two-class layout (or for over 140 in a high-density single-class layout as typical from the 1960s onwards on inclusive-tour charter flights). The design initially included a cruciform tail layout similar to that of the Sud Aviation Caravelle. The engines were clustered at the rear, with the centre engine situated in the extreme rear of the fuselage fed by air ducted through a large oval intake at the front of the fin, a configuration similar to the later Boeing 727. The design eventually settled on a variable-incidence T-tail.
From the outset the D.H.121 was planned to employ avionics which 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 flightdeck; the compartment's size was among the factors dictating a distinctive nose undercarriage design: offset by 2 ft (61 cm) to the port side and retracting sideways to stow across the D.H.121's longitudinal axis.
In 1958, BEA concluded that the D.H.121's payload-range capacity was too great for their needs and petitioned de Havilland to reduce the scale of the design to suit their revised projections. In 1959 BEA had a large fleet in operation and on order, and the issue of overcapacity was a critical concern. 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 D.H.121's general payload-range area, and the growing trend to higher-density seating. At the time, many reputable airlines were reducing their short/medium range seat pitches from the then-customary minimum of 36 in (91 cm) to 34 in (86 cm) or less.
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": a sentiment which would be echoed throughout the Trident's subsequent history. It was, however, noted that de Havilland had not yet secured a formal and final BEA order and that its competitor Bristol was actively promoting their 200 [N 3] project, which was significantly smaller than the D.H.121. At the time Boeing and Douglas were also downsizing their DC-9 and 727 projects. It was felt the original large D.H.121 would have to compete against the Convair 880 and Boeing 720 some four years after their service entries, whereas a cut-back design would be more competitive against the then-projected 75–100 seat, twin-engined DC-9.
Downsizing the Trident involved substantial changes, including a powerplant change from the Medway to a scaled-down derivative, the 40 percent less powerful 9,850 lbf (43.8 kN) Rolls-Royce Spey 505. The gross weight was cut by about a third to 105,000 pounds (48,000 kilograms), range was cut by more than half to 930 miles (1,500 kilometres), and mixed-class seating was cut by about a quarter to 75 or 80 (97 in a single-class layout). Wing span was reduced by approximately 17 ft (5.2 m), wing area by 30 percent and overall length by 13 ft (4.0 m). The revised design retained some features of the original one, notably fuselage diameter. It had a smaller flightdeck and single-axis, two-wheel, four-tyre main undercarriage legs in place of four-wheel bogies.
Details of the emerging aircraft, including its pioneering avionics, were announced to the public in early 1960. It was this revised aircraft that BEA ultimately ordered on 24 August 1959, initially in 24 examples with 12 options. The future airliner's name, Trident, was announced at the Farnborough Airshow in September 1960, as a reflection of its then-unique three-jet, triple-hydraulic layout.
Industry consolidation and competition
While the D.H.121 emerged in the late 1950s, British government viewed the airframe and aeroengine industries as too fragmented into small companies. Government accordingly elaborated a policy favouring mergers into a few large groups. Accordingly, de Havilland consorted with Hunting Aircraft and Fairey Aviation to manufacture and market the D.H.121 under the corporate name of defunct Airco, after Geoffrey de Havilland's employer during World War I. The Minister of Supply, however, stated of the Airco consortium that "this is not quite what [he] had in mind". By 1960, de Havilland (along with Blackburn) had been acquired by the Hawker Siddeley group.
Airco executives intensively explored alternatives to the merger, such as the possibility that Boeing may drop its 727 project and instead manufacture Airco D.H.121s in the USA. This involved two Airco visits to Boeing and a return visit by Boeing executives and engineers. British commentators have tended to interpret this episode as involving the acquisition of sensitive proprietary data on the D.H.121 by a direct competitor. After the de Havilland takeover by Hawker Siddeley, 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 D.H.121 as a complementary, smaller member of the same airliner family. Fairey Aviation, partially incorporated into Westland Aircraft, also left the D.H.121 project. [N 4] With the move to Hawker Siddeley Aviation, the designation eventually changed to the HS 121.
Industry reorganisation added to delays caused by BEA's specification changes, hurting the Trident's competitiveness against the Boeing 727. An example is Trans Australia Airlines which determined the Trident to be superior to the Boeing 727 from an operational standpoint, however it was viewed as commercially risky to choose a different fleet from rivals like Ansett Australia, who had selected the 727.
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, aspirating through an S-shaped duct. One version, the 3B, had a fourth "boost" engine aspirated through 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 also by Rolls-Royce: the RB.162, originally intended as a lift engine for VTOL applications.
The Trident was one of the fastest subsonic commercial airliners, regularly cruising at over 610 mph (980 km/h). At introduction into service its standard cruise Mach Number was 0.88/ 380kts IAS, probably the highest of any of its contemporaries. 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 power-to-weight ratio, called for prolonged takeoff runs. Nevertheless, the Trident fulfilled BEA's 6,000 ft (1,800 m) 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 4,500 ft (1,400 m) field length criteria.
The Trident was routinely able to descend at rates of up to 4500 ft/min (23 m/s) in regular service. In emergency descents it was permissible to use reverse thrust of up to 10,000 rpm. Below 280 kt 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.
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 = 200 ft (61 m) 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.
The Trident's advanced avionics displayed the aircraft's momentary position relative to the ground on a moving map display on the centre instrument panel. This electro-mechanical device also recorded the aircraft's track using a stylus plotting on a motor-driven paper map. Positional information was given by a Doppler navigation system which read groundspeed and drift data which, alongside heading data, drove the stylus.
The Trident was the first airliner fitted with a quick access flight data recorder. This sampled 13 variables, converted them into a digital format and stored them on magnetic tape for ground analysis.
Hawker Siddeley Aviation, which had absorbed de Havilland, needed additional customers for the Trident, so entered into discussions with American Airlines (AA) in 1960. American demanded an aircraft with a longer range, which meant that the original DH121 design would have fulfilled its requirements almost perfectly. To fill AA's needs, design began on a new Trident 1A, powered with uprated Rolls-Royce Spey 510s of 10,700 lbf (47.6 kN) thrust, and a larger wing with more fuel, raising gross weight to 120,000 lb (54,000 kg) and range to 1,800 miles (2,900 kilometres). AA eventually declined the aircraft in favour of the Boeing 727, an aircraft that filled the original DH121 specifications almost exactly.
Some of these changes were nevertheless added into the original prototype, and it was renamed the Trident 1C. The main difference was a larger fuel tank in the centre section of the wing, raising weights to 115,000 lb (52,000 kg) and range to 1,400 miles (2,300 kilometres). The first Trident 1, G-ARPA, made its maiden flight on 9 January 1962 from Hatfield Aerodrome, and entered service on 1 April 1964. By 1965, there were 15 Tridents in BEA's fleet and by March 1966, the fleet had increased to 21.
Hawker Siddeley then proposed an improved 1C, the Trident 1E. This would use 11,400 lbf (50.7 kN) Spey 511s, have a gross weight of 128,000 lb (58,000 kg), an increased wing area by extending the chord, and the same fuselage but with up to 140 seats in a six-abreast configuration. This specification took the 1C closer to the larger concept of the original DH121, but powered with 7,000 lbf (31 kN) less thrust. There were only a few sales of the new design: three each for Kuwait Airways and Iraqi Airways, four for Pakistan International Airlines (later sold to CAAC), two each for Channel Airways and Northeast Airlines, and one for Air Ceylon. Channel Airways' aircraft were operated with cramped, 21" pitch, seven-abreast seating in the forward section.
At this point, BEA decided that the Trident was now too short-legged for its ever-expanding routes, and that an even longer-ranged version was needed. Hawker Siddeley responded with another upgrade as the Trident 1F. It would have the Spey 511 engines, a 2.8 m fuselage stretch, a gross weight of 132,000 lb (60,000 kg) and up to 128 seats in the original five-abreast configuration. BEA planned to buy 10 1Fs, plus an option for 14 further aircraft.
As work continued on the 1F the changes became so widespread that it was renamed the Trident 2E, E for Extended Range. Now powered by newer Spey 512s with 11,930 lbf (53.1 kN) thrust, it also replaced wing leading-edge droops with slats, and extended the span with Küchemann-style tips. It had a gross weight of 142,400 lb (64,600 kg) and a 2,000 miles (3,200 kilometres) range.
BEA bought fifteen, while two were bought by Cyprus Airways. CAAC, the Chinese national airline, bought 33. The first flight of this version was made on 27 July 1967 and it entered service with BEA in April 1968.
Subsequently, the Trident was becoming the backbone of the BEA fleet and BEA wanted an even larger aircraft. Hawker Siddeley 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 and led to a modern-looking design very similar to the Boeing 757. 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 role of both the BAC 1–11 and Trident, but this plan was vetoed by the British government.
BEA returned to Hawker Siddeley and instead chose a stretched version of the basic Trident, the Trident 3. A fuselage stretch of 5 m (16 ft 5 in) made room for up to 180 passengers; Hawker Siddeley raised the gross weight to 143,000 lb (65,000 kg) 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 issues experienced on 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 completely different type, which would have been difficult for the engine buried in the tail, Hawker Siddeley'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% more thrust for takeoff, while adding only 5% more weight, and 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 would eventually be sold.
In 1977, fatigue cracks were discovered in the wings of the British Airways Trident fleet. The aircraft were ferried back to the manufacturer, and repaired, then returned to service. On 1 January 1986, new ICAO noise legislation came into force, requiring operators of first and second generation jet airlines have hush kits fitted to their engines; the main British operator of the type in that era, British Airways, viewed the required refit as unviable and instead chose to phase the Trident out of its fleet. In total, 117 Tridents were produced, while the Boeing 727, built to the original airline specification for the Trident, sold 1,832 units.
- Trident 1C
- Production version for British European Airways, 24 built
- Trident 1E
- Increased seating capacity uprated engines and addition of leading edge slats, 15 built
- Trident 2E
- As Trident 1E version with triplex autoland system, 50 built
- Trident 3B
- High-capacity short-medium range version of the 2E with a 16 ft 5 in (5.00 m) stretch, 1 RB.162 booster engine in the tail; 26 built
- Super Trident 3B
- Extended range by 692 (430) miles, two built
- Air Charter Service of Zaire
Aircraft on display
- Trident 1C G-ARPO Save the Trident Group at North East Aircraft Museum, Sunderland, UK. This is the last 1C Trident to be completed.
- Trident 1E "B-2207" at the Military Museum of the Chinese People's Revolution, Beijing, China.
- Trident 2E G-AVFB at Duxford, UK
- Trident 3B G-AWZK in Aviation Viewing Park at Manchester Airport, Manchester, UK; moved from Heathrow in September 2005 (clipped wings).
- Trident 3B G-AWZM at Science Museum's exhibit store at Wroughton in Wiltshire, UK
- Trident 2E 5B-DAB at Nicosia International Airport (derelict). As of 2015 the aircraft was still in existence, having stood for 35 years.
- Trident 2E G-AVFE on the fire ground at Belfast International Airport (complete).
- Trident 3B G-AWZS at International fire training centre Teesside Airport (complete).
Several aircraft or sections in use as fire service training aids and aircraft either preserved or in storage at various locations in China (three airframes, one with a broken back, can be seen at the Beijing Aeroplane Museum at Datangshan, north of Beijing). In 2008, the personal aircraft of Mao Zedong was offered for sale after a decision by merchants at a market in Zhuhai that the Trident, formerly a tourist attraction, was limiting business.
- On 3 June 1966, Trident 1C G-ARPY entered into a deep stall while on a test flight and crashed at Felthorpe, Norfolk, killing all four crew.
- On 30 June 1966, Trident 1E registration 9K-ACG touched down 3 miles short of the runway at Kuwait International Airport. There were no fatalities but the aircraft was written off.
- On 3 July 1968, Trident 1s G-ARPI and G-ARPT were struck by Airspeed Ambassador G-AMAD, which crashed at London Heathrow Airport due to the failure of a flap operating rod. G-ARPI was severely damaged, but repaired and returned to service, whereas G-ARPT was written off.
- 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. Official PRC accounts claim that the Trident ran out of fuel.
- On 18 June 1972, British European Airways Flight 548, a Trident 1, G-ARPI, stalled due to pilot error and crashed at Staines shortly after takeoff from Heathrow Airport. All 118 on board were killed and it became known as the "Staines air disaster". As of 2016, it is still the worst aviation accident to have occurred on British soil (Pan Am Flight 103 was a terrorist incident).
- On 10 September 1976, a British Airways Trident 3B, G-AWZT, collided in midair with an Inex Adria McDonnell-Douglas DC-9, 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 Trident 2E, 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. Total fatalities were all 12 crew, 32 ground, and no passengers.
- On 26 April 1982, CAAC Flight 3303 Trident 2E, B-266 crashed near Yangsuo, China killing all 112 passengers and crew.
- 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 then struck a lip and collapsed, causing the aircraft to run off the runway and slip into the harbour. Seven people were killed.
|Trident 1||Trident 1C||Trident 1E||Trident 2E||Trident 3B|
|Cockpit Crew||Three (Captain, First Officer and System Panel Operator)|
|Seating Capacity (Typical)||101 Passengers||108 Passengers||115 Passengers||180 Passengers|
|Length||114 ft 9 in (34.98 m)||131 ft 2 in (39.98 m)|
|Wingspan||89 ft 10 in (27.38 m)||95 ft (29 m)||98 ft (30 m)|
|Wing Area||1,358 sq ft (126.2 m2)||1,415 sq ft (131.5 m2)||1,462 sq ft (135.8 m2)|
|Wing Sweepback||35 degrees|
|Overall Height||27 ft 0 in (8.23 m)||28 ft 3 in (8.61 m)|
|Maximum Cabin Width||11 ft 3.5 in (3.442 m)|
|Operating Empty Weight, typical||66,700 lb (30,300 kg)||67,200 lb (30,500 kg)||70,000 lb (32,000 kg)||73,200 lb (33,200 kg)||83,000 lb (38,000 kg)|
|Maximum Takeoff Weight||107,000 lb (49,000 kg)||115,000 lb (52,000 kg)||128,000 lb (58,000 kg)||142,500 lb (64,600 kg)||150,000 lb (68,000 kg)|
|Cruise Speed||Mach 0.86 - 506 kn (582 mph; 937 km/h) at 30,000 ft (9,100 m)||Mach 0.84 - 495 kn (570 mph; 917 km/h) at 30,000 ft (9,100 m)|
|Range||1,350 mi (1,170 nmi; 2,170 km)||2,025 mi (1,760 nmi; 3,259 km)||2,200 mi (1,900 nmi; 3,500 km)||2,700 mi (2,300 nmi; 4,300 km)||2,235 mi (1,942 nmi; 3,597 km)|
|Fuel Capacity||3,840 imp gal (17,500 l; 4,610 US gal)||4,840 imp gal (22,000 l; 5,810 US gal)||5,440 imp gal (24,700 l; 6,530 US gal)||5,774 imp gal (26,250 l; 6,934 US gal)||5,440 imp gal (24,700 l; 6,530 US gal)|
|Service Ceiling||35,000 ft (11,000 m)|
|Powerplant||3 x Rolls Royce Spey RB163-1 Mk505-5||3 x Rolls Royce Spey RB163-25 Mk511-5||3 x Rolls Royce Spey RB163-25 Mk512-5||3 x Rolls Royce Spey RB163-25 Mk512-5 + 1 x Rolls-Royce RB162-86 Booster|
|Thrust||3 x 10,400 lbf (46 kN)||3 x 11,400 lbf (51 kN)||3 x 11,960 lbf (53.2 kN)||3 x 11,960 lbf (53.2 kN) Booster: 5,250 lbf (23.4 kN)|
- Aircraft of comparable role, configuration and era
- Related lists
- British aviation writer Bill Gunston was influential in elaborating this discourse.
- "B.E.A.'s feelings on these points were not inflexible. Their specification constituted a basis for discussion ..."
- redesignated the Bristol 205
- Hunting and Fairey remained D.H.121 subcontractors.
- Kenward, Michael. "Cutting through the fog with autoland." New Scientist, 10 February 1972. pp. 321–323.
- Bearup, Benjamin. "Flashback Friday: 50th Anniversary of Autolanding." Airways News, 31 July 2015.
- Jerram and Barnet, 1981
- "Hawker Siddeley Mergers." Flight International, 12 February 1960, p. 196.
- Staniland 2003, p. 149.
- Munson 1967, pp. 153–154.
- ""Thoughts on the D.H.121." Flight International 28 February 1958, p. 267.
- "Airco D.H.121". Flight International, 25 July 1958.
- "Bristol 200 – a Preliminary Appraisal." Flight International, 24 January 1958, p. 109.
- "B.E.A.'s Jet: Cards on the Table." Flight International, February 1958, p. 167.
- Staniland 2003, pp. 149–150.
- "Deep-Stall Avoidance." Concept to Reality. Retrieved: 13 November 2010.
- "Touchdown by Computer." Time Magazine, 18 June 1965. Retrieved: 17 July 2009.
- Staniland 2003, p. 150.
- "B.E.A. versus Traffic Recession." Flight International, 28 August 1958, p. 74.
- "Subsonic Setback?" Flight International, 29 May 1959, p. 753.
- "A Smaller D.H.121." Flight International, 14 August 1959, p. 26.
- "Airco D.H.121: Preliminary Details." Flight International, 28 August 1959, p. 91.
- "D.H.121: Progress Report on Britain's 600 m.p.h. Viscount Replacement." Flight International 22 January 1960, p. 102.
- "The D.H.121 and Automatic Landing." Flight International, 22 January 1960, p. 120.
- "Commercial Aircraft of the World: D.H.121 Trident Mk 1." 'Flight International, 18 November 1960, p. 798.
- Bacon, Roger. "Straight & Level." Flight International, 16 December 1960, p. 953.
- Gunn 1999, pp. 184–185.
- "Talking to Mr. Beall: Boeing's Senior Vice-President in London." Flight International, 14 October 1960, p. 603.
- Pratt, Roger, ed. Flight Control Systems: Practical Issues in Design and Implementation. Kidlington, Oxfordshire, UK: Elsevier Science Ltd., 2000. ISBN 0-85296-766-7.
- "Trident Automatically." Flight International, 17 June 1965, p. 972.
- Jackson 1973, pp. 272–276.
- "Smiths Industries Flight Data/Cockpit Voice Recorders." ntsb.gov. Retrieved: 1 April 2010.
- "BEA orders more Tridents." Glasgow Herald, 6 August 1965.
- "British bid to sell jets to China." The Age, 10 May 1971.
- "After Trident, Concorde?" Glasgow Herald, 5 December 1973.
- Imrie, Ian. "New snag could again delay Tridents." Glasgow Herald, 12 August 1977.
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- "Iconic plane on show after five-year restoration." Northern Echo, 3 July 2015.
- Aviation Museums
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- "Criminal Occurrence description: Trident 1E crash, 13 September 1971." aviation-safety.net. Retrieved: 13 November 2010.
- Civil Aircraft Accident Report 4/73: Trident I G-ARPI: Report of the Public Inquiry into the Causes and Circumstances of the Accident near Staines on 18 June 1972 – Appendix A Accident Investigation Branch, Department of Trade and Industry. HMSO, London, 1973.
- "Accident description: Hawker Siddeley HS-121 Trident 1C, 18 June 1972." aviation-safety.net. Retrieved: 13 November 2010.
- "Accident description: Hawker Siddeley HS-121 Trident 3B, 10 September 1976." aviation-safety.net. Retrieved: 13 November 2010.
- "CAAC Trident 2E." planecrashinfo.com. Retrieved: 1 April 2010.
- "ASN Aircraft accident: Hawker Siddeley HS-121 Trident 2E B-266 Yangsuo." aviation-safety.net. Retrieved: 1 April 2010.
- "Accident description: Hawker Siddeley HS-121 Trident 2E, 31 August 1988." aviation-safety.net. Retrieved: 13 November 2010.
- Jackson 1973, p. 276.
- Green 1976, p. 117.
- Green, William. The Observer's Book of Aircraft. London: Frederick Warne & Co. Ltd., 1976. ISBN 0-7232-1553-7.
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