On 10 June 1965, a British airliner full of fare-paying passengers came down the approach to a runway and landed without either pilot touching the controls. It was the first automatic landing by a civil airliner in scheduled passenger service, and it happened on an aeroplane most people outside Britain have never heard of.

The Hawker Siddeley Trident should have been Britain's Boeing 727. It was faster, it was cleverer, and it got there first on almost every technology that mattered. It sold 117 aircraft. The 727 sold into four figures. The story of how that happened is one of the most instructive in commercial aviation.

An airline that did not want jets

The Trident exists because British European Airways asked for it, and very nearly did not. In 1953 BEA had just put the world's first turboprop airliner into service and was convinced propellers were the sensible future. Its chief executive was blunt about the alternative.

What changed his mind was French. The Sud Aviation Caravelle had flown and was shaping up to be a serious competitor, and BEA realised it needed something quicker.

In July 1956 the airline issued “outline requirements” for a short-haul second-generation jet: roughly 70 passengers, 1,000 miles, 6,000-foot runways, a very high cruise, and — this mattered enormously — “more than two engines”. De Havilland answered in 1957 with the DH.121, the world's first trijet airliner design, sized for around 111 passengers and built around the powerful Rolls-Royce Medway.

The decision that cost Britain the market

Then BEA changed its mind. Facing a downturn, the airline decided it wanted a smaller, shorter-ranged aeroplane, and de Havilland obliged. The Medway was dropped for the less powerful Spey, and the aircraft was shrunk to suit one customer's revised forecast.

Boeing, designing the 727 at the same moment, did the opposite. It built an aircraft sized for a market rather than for an airline, and gave it the field performance to operate almost anywhere. When the Trident entered service in April 1964, the 727 had beaten it by two months and offered more seats, more range and shorter runway requirements.

The Trident was also a demanding aeroplane on a hot day. The wing was optimised for a critical Mach number of 0.93 and produced relatively little lift at low speed; combined with a modest thrust-to-weight ratio, that meant long takeoff runs. It met BEA's 6,000-foot criterion. It could not meet the 4,500-foot standard the world moved to.

The part where it was decades ahead

None of which should obscure what the Trident actually achieved. Hawker Siddeley and Smiths Aircraft Instruments built it a fully automatic blind landing system capable of flying the approach, the flare, the touchdown and the roll-out.

The world's first autoland in scheduled service came on 10 June 1965. The first genuinely blind landing followed on 4 November 1966. The Trident pioneered Category 2 minima — a 100-foot decision height and 400 metres of runway visual range — and then went to Category 3C, the “zero-zero” condition.

The practical effect at a foggy Heathrow was dramatic. When other airlines were diverting, BEA's Tridents kept landing.

The avionics did not stop at autoland. The Trident had a moving map on the centre panel, a stylus plotting the aircraft's track on a motor-driven paper chart, driven by Doppler groundspeed and drift data. It was also the first airliner fitted with a quick access flight data recorder, sampling 64 variables digitally onto magnetic tape for analysis on the ground — the direct ancestor of modern flight data monitoring.

The wing that outlived the aeroplane

The Trident's aerodynamics were developed by a team under Richard Clarkson, who won the Mullard Award in 1969 for the work. He later used the Trident wing as the starting point for the wing of the Airbus A300.

So the aircraft that lost the short-haul market to Boeing quietly seeded the wing of the aircraft that started Airbus. The Trident was withdrawn in 1995 after a 31-year career. Its real legacy is not in the sales figures. It is that every time an airliner lands itself in fog today, it is doing something a British trijet did first, in front of passengers, in 1965.

Sources: Wikipedia, Key.Aero, The British Airliner Collection, and BEA archive film.