Hawker Siddley Trident 2E
Hawker Siddley Trident 2E, G-AVFI, 2148 at Farnborough Airshow 1968
The Hawker Siddeley HS 121 Trident (originally the de Havilland D.H.121 and the Airco DH 121) was a British short and medium-range airliner. It was the first T-tail rear-engined three-engined jet airliner designed. It was also the first airliner to make a blind landing in revenue service in 1965.
By the end of the programme in 1978, 117 Tridents were produced. BEA's successor British Airways withdrew its Tridents by the mid-1980s. Trident services ended in China in the early 1990s.
The ability to land in fog solved a major problem at London Heathrow and other British airports. Delays were commonplace when Category 1 (Cat 1 = 200 ft (61 m) decision height and 600 metre runway visual range RVR) instrument landing system (ILS) was in use. The Trident's autoland system pioneered the use of lower landing minimums, initially with Category 2 (100 ft decision height and 400 metres RVR) and soon being allowed to undertake "zero-zero" (Category 3C) operations. Because the Trident fleet could operate safely to airfields equipped with suitable ILS installations, it could operate as scheduled irrespective of weather, while other aircraft were forced to divert.
The Trident's advanced avionics displayed the aircraft's momentary position relative to the ground on a moving map display on the centre instrument panel. This electro-mechanical device also recorded the aircraft's track using a stylus plotting on a motor-driven paper map. Positional information was derived from a doppler navigation system which read groundspeed and drift data which, alongside heading data, drove the stylus.
The Trident was the first airliner fitted with a quick access flight data recorder. This sampled 13 variables, converted them into a digital format and stored them on magnetic tape for ground analysis.
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Old slide scan.