In March 1959, BEA, which had become concerned by a recent decline in passenger growth, concluded that the D.H.121's payload-range capacity could be too great for their needs and petitioned de Havilland to reduce the scale of the design to suit their revised projections.
Fearing that the proposed scale of the Trident was too large, the airline had elected to effectively tear up the programme for its redesigning for their immediate situation.
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.

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.
The de Havilland board elected to submit to BEA's demand, over-riding input from its own sales and market research departments which indicated that other airlines sought the larger model instead.
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  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 to the design being made, 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), while the 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 its fuselage diameter.
It had a smaller flightdeck and single-axis, two-wheel, four-tyre main undercarriage legs in place of four-wheel bogies.
Woods summarised the BEA-mandated redesign as: "At one blow the 121 was emasculated in terms of size, power and range".

Six months following BEA's request, de Havilland and the airline came to an agreement on the downsized D.H.121.
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.
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.
In March 1959, BEA, which had become concerned by a recent decline in passenger growth, concluded that the D.H.121's payload-range capacity could be too great for their needs and petitioned de Havilland to reduce the scale of the design to suit their revised projections. Fearing that the proposed scale of the Trident was too large, the airline had elected to effectively tear up the programme for its redesigning for their immediate situation. 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.
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. The de Havilland board elected to submit to BEA's demand, over-riding input from its own sales and market research departments which indicated that other airlines sought the larger model instead. 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  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 to the design being made, 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), while the 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 its fuselage diameter. It had a smaller flightdeck and single-axis, two-wheel, four-tyre main undercarriage legs in place of four-wheel bogies. Woods summarised the BEA-mandated redesign as: "At one blow the 121 was emasculated in terms of size, power and range".
Six months following BEA's request, de Havilland and the airline came to an agreement on the downsized D.H.121. 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. 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.
Hawker Siddeley Trident