The Hawker Siddeley HS-121 Trident (originally the de Havilland DH.121 and briefly the Airco DH.121) is a British airliner produced by Hawker Siddeley.
In 1957, de Havilland proposed its DH.121 trijet design to a British European Airways (BEA) request. By 1960, de Havilland had been acquired by Hawker Siddeley. The Trident's maiden flight happened on 9 January 1962, and it was introduced on 1 April 1964, two months after its main competitor, the Boeing 727. By the end of the programme in 1978, 117 Tridents had been produced. The Trident was withdrawn from service in 1995.
The jetliner is powered by three rear-mounted Rolls-Royce Spey low-bypass turbofans, it has a low swept wing and a T-tail. Advanced avionics allowed it to be the first airliner to make a blind landing in revenue service in 1965.
The initial Trident 1/2 could seat 101-115 passengers over up to . The Trident 3 was stretched by to seat 180 over , and had an additional RB.162 booster engine in the tail.
Development
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 370 knots. 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. In July 1956, BEA had announced what it called "outline requirements" for a short-haul "second-generation jet airliner", to work alongside its turboprop fleet. It would carry a payload of some or some 70 passengers up to , weigh about , use runways, cruise at a very high speed of , and have "more than two engines". 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.
Four companies prepared projects to match the BEA outline. Bristol proposed the initially four-engined Bristol Type 200. Avro proposed the futuristic Avro 740 trijet before shelving it and joining forces with Bristol and Hawker Siddeley. Vickers proposed the VC11 four-engined airliner, derived from its in-development VC10. The company considered three possible contenders for the specification; two of these were four-engined developments of the early Comet, the world's first jet-powered airliner: the D.H.119 and the D.H.120, the latter being also intended to be offered to British Overseas Airways Corporation (BOAC). In July 1957, de Havilland made another submission in the form of the DH.121; this proposal was furnished with three turbojets, Rolls-Royce Avon engines, and greatly resembled the eventual production aircraft. 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.