Hawker Siddeley Trident — 60 years.

The prototype Hawker Siddeley Trident made its maiden flight from Hatfield, the UK in 1962.

The airliner was initially known as the DI-1121, conceived by the De Havilland Aircraft Company. The jet was revolutionary in British aviation and was also the world's first trijet.

One of the earliest airlines to show an interest was American Airlines (AA).
De Havilland adapted the design to suit the carrier's needs. However, American Airlines decided to select the rival Boeing 727, an aircraft they said 'matched its requirement perfectly.'

De Havilland then adapted the design to suit UK carrier British European Airways (BEA). Powered by Rolls-Royce Spey engines, the manufacturer planned to offer advanced avionics for time, including automatic approach and landing capabilities. The Smiths Aircraft Industries Autoland System feature enabled pilots to operate in even the worst visibility conditions.

Before the aircraft took to the air, a reorganization of the British aircraft industry saw De Havilland merge into Hawker Siddeley Group. The DI-1121 was subsequently rebranded as the HS121 Trident.

The new owners would go on to design several variants of the aircraft: Trident 1C (24 built), Trident 1E (15 built), Trident 2E (50 built), Trident 3B (26 built) and the Super Trident 3B (two built).

The earlier adaption of the airliner specifically for BEA meant the Trident lacked the range and short field performance capabilities to compete with the 727.

However, one market where the aircraft saw success was China. The Civil Aviation Administration of China (CAAC) received its first Trident in 1970. From here, the carrier would receive 33 factory-fresh 2Es and both Super Trident 3Bs constructed. The airline would use the jet into the 1990s. China regarded it as "the best aircraft the west had ever produced."