Originally designed by the de Havilland Aircraft Company under the designation DH.121, the Trident was a revolutionary ‘Tri-liner’ design featuring three-engines and a T-tail, never seen before on a UK aircraft. American Airlines were one of the first operators to show interest in the Trident concept and to meet their requirements de Havilland designed the DH.121 Trident 1A, combining the required long-range capability with the powerful Rolls-Royce Medway engines and an appropriately increased fuel capacity. Eventually however, and to much disappointment at Hatfield, American Airlines selected the Boeing 727 which 'matched its requirement perfectly'.
de Havilland immediately adapted its initial design and built an aircraft to directly reflect the specifications of the domestic carrier, British European Airways (BEA), complete with the Rolls-Royce Spey engines which would feature on every variant thereafter. The first full prototype, designated DH.121 Trident 1C (G-ARPA), flew for the first time at Hatfield on 9th January 1962.
Configured for air routes within Western Europe, the Trident was compromised by its strict BEA specification and according to most prospective customers it was 'lacking range and short field performance'. This was particularly evident when compared with its US rival, the Boeing 727, which by now was beginning to dominate this emerging and valuable market.
The initial production run was for 24 DH.121 Trident 1Cs for BEA, who also took out an option on a further 12 aircraft. From the outset the DH.121 Trident was planned to incorporate the very latest in avionics and within a few years of operation it had pioneered the revolutionary Smiths Aircraft Industries 'Autoland' System (which allowed for continued operations in effectively zero visibility), thus increasing its in service and winter reliability.
During the development cycle of the aircraft, de Havilland was subject to the rationalisation of the British aircraft industry which saw the company merge into the Hawker Siddeley Group. As a result, the designation of the aircraft was changed to the Hawker Siddeley HS121. Delays created by the re-organisation and the overall upheaval saw HS121 Tridents lose out to Boeing 727s on more than one occasion, many prospective buyers deciding that delivery promises were 'commercially, too risky'.
Hawker Siddeley then introduced the HS121 Trident 1E which offered increased passenger capacity (115-139), and a much-increased fuel capacity. Many observers commented that the aircraft was now much closer in specification to the original Trident 1A configuration although in the end only 15 were built, operating with Kuwait Airways, Iraqi Airways and Pakistan International Airlines. Other operators included Channel Airways, Northeast Airlines, Air Ceylon and Cyprus Airways (who chose a very cramped 7-across seat pattern).
By now the mood was changing within BEA who had started to investigate longer routes. This caused another re-think at Hawker Siddeley who responded with the Trident 1F. However, as work started and various changes were made to the Trident 1F package, it was soon concluded that it would be renamed Trident 2E (the E standing for ‘Extended Range’).
The first HS121 Trident 2E flew on 27th July 1967 and featured an increase in fuel capacity. This, combined with more powerful engines and increased take-off weight, allowed the type to offer both a greater passenger capacity and longer range. 50 aircraft were built, serving with BEA (15 aircraft), China’s Civil Aviation Administration of China (33 aircraft) and Cyprus Airways (2 aircraft). The BEA Tridents became the mainstay of the BEA operations and it wasn’t long before they were asking for an even bigger aircraft. Initially, Hawker Siddeley offered two designs: the HS132 (158 seater) and the HS134 (185 seater). Both designs departed from the tri-jet design concept of the Trident by relocating the engines under the wings. Unfortunately, this found little favour with the airlines and BEA opted for the Boeing 727 and 737 to fill the previous roles met by its HS-121Tridents and BAC1-11’s. However, when these plans were blocked by the British government, BEA were forced to return to Hawker Siddeley who responded with an even more stretched version of the basic Trident, known this time as the HS-121 Trident 3.
Around five metres longer than the previous version, the Trident 3B could carry up to 180 passengers and although the engines remained the same, the wings were cleverly reconfigured to handle the increased weight. BEA initially rejected the Trident 3 design as being unable to perform in ‘hot and high’ conditions. In response, and rather than replacing the three Spey engines, Hawker Siddeley decided to add a ‘fourth engine’ into the tail with the placement the Rolls-Royce RB162, a tiny turbo-jet. This gave the aircraft the 15% increase in take-off power needed to avert criticism and the first Trident 3B flew on 11th December 1969.
Twenty-six aircraft were built for BEA with two additional HS121 Trident ‘Super 3B’ aircraft being delivered to the Civil Aviation Administration of China (CAAC) with maximum weight raised to 158,000 lb. China became a key export customer for the Trident and eventually some 35 aircraft went into service in the People’s Republic.
With its low by-pass engines, the Trident was undoubtedly noisy and the advent of more stringent International Civil Aviation Organization (ICAO) noise regulations, introduced in January 1986, contributed to its early withdrawal from airline service. By then BEA had been consumed by British Airways, who concluded that it was not viable to convert their Trident fleet and embarked on a program of phased-retirement. The CAAC were however still committed to the aircraft, and it continued to operate their fleet in China until the early 1990s, with the aircraft finally being withdrawn from service in 1995.