And finally something new - another 'big story'
DHBC Breaks (Almost) Big - the Trident
Airlines in British Columbia, particularly Air BC and Inter-Dominion, closely followed the developments in the United Kingdom surrounding the British European Airways requirement for a new jet airliner. Shortly after De Havilland UK proposed the DH.121 in 1957, it was proposed that DHBC might produce the type for the North American market. Letters of intent were signed by BEA for 24 Tridents and by Inter-Dominion for 25 in 1958, which got the project underway. However, when BEA modified its requirements and persuaded DH to make a smaller aircraft, IDAL withdrew its interest.
After some negotiation, however, it was agreed that DHBC would take over development of the larger design; since the smaller DH.121 Trident - this name was announced at the Farnborough Airshow of 1960 - was to use the smaller Spey engine, Hoffar Aero Engines acquired a licence to build the Rolls-Royce RB.141 Medway engine that had been intended for the larger design. Restructuring of the British aviation industry - which led to the complete independence of De Havilland BC in 1961 - caused some delays, but in the same year the DHBC project was formally designated DHBC-7 Trident. Despite the division of effort, however, much work was undertaken jointly by DHUK and DHBC, with the result that the British Trident 1 and the British Columbian Trident 7 shared a great deal in common, to the extent that there was a high degree of parts commonality between the two types.
Although the Trident 1 undertook its first flight in January 1962, it was another four years until the Trident 7A first took to the sky.
DHBC-7 Trident 7AThe Trident was groundbreaking in many ways, being the first aircraft in the world capable of landing in below-minimum (Category II) conditions. This autoland system was operated by three independent autopiilots capable of guiding the aircraft automatically during airfield approach, flare, touchdown and even roll-out from the landing runway, which made it possible to operate the Trident when other aircraft were forced to divert. The three-person cockpit crew was also assisted by an innovative moving-map system displaying the aircraft's momentary position, and was the first aircraft to be fitted with a quick-access flight data recorder. The standard equipment fit included two VOR-ILS systems, dual ADF, HF and VHF radios (the HF radio equipped with SELCAL), three radio altimeters, a transponder, and weather radar.
The three engines were located in the aft section of the fuselage, two in nacelles mounted on either side, with the third in the centre on the same plane as the outboard engines; air was supplied to the centre engine via an intake mounted atop the fuselage at the base of the vertical stabiliser via an S-duct. Only the nacelle-mounted engines were fitted with thrust reversers. Each Rolls-Royce/Hoffar RB.141 Medway engines of the Trident 7A operated an independent hydraulic system via an engine-driven pump powering nose wheel steering, brakes, undercarriage, and all flight surfaces; two electrically driven pumps were supplied as a backup for the hydraulic system.
A Garrett AiResearch GTCP-85 APU was fitted in a fairing at the base of the vertical stabiliser above the centre engine to run the air conditioning system, start the engines, and drive generators to supply electric power on the ground; the APU could be operated in flight to drive the hydraulic backup pumps. Initially a distinctive feature of the BC Trident, the fairing-mounted APU was later added to the British Trident 2E.
Aside from the latter being ten feet longer, the greatest difference between the Trident 1 and the 7A was in the wings. Whilst the 1 had a span of 89' 10", the wing of the 7A was based on that of the Trident 1E of 1965, which had a 95 foot wingspan and surface area of 1,446 square feet; the DHBC designers took this a step further, increasing the span to 98 feet and an area of 1,462 square feet by adding Küchemann wingtips to the 1E design - this design was used by Hawker Siddeley on the Trident 2E and 3B. They were made of aluminium alloy stringers and skins of continuous wingtip-to-wingtip construction with a six-cell centre section box across the fuselage, a two-cell box from the wing root to a point at 40% of the span, and a single-cell box from there to the wingtip. The wings featured full-length leading edge slats and three-section double-slotted trailing edge flaps and ailerons of metal construction; the forward outboard flap acted as an airbrake, whilst the forward inner flap served as a spoiler or lift dumper. The leading and trailing edge devices were operated by off three independent hydraulic systems, of which only one was needed for full activation; there was no provision for manual reversion. Fuel was stored in five wing-internal tanks - two in each wing and one in the wing centre section; pressure fuelling was completed via a single point on each wing.
The tailplane of the Trident 7A was fifteen inches taller than that of the Trident 1; this was another DHBC feature adopted by Hawker Siddeley, in this case on the Trident 3B. It had an all-metal vertical surface with a rudder and an all-moving horizontal stabiliser with geared and slotted trailing edge flaps without trim tabs.
The undercarriage was arranged in a tricycle configuration. The twin-wheel nose gear, fitted with a Lockheed oleo-pneumatic shock absorber, was offset two feet from the centreline to retract sideways into its well; this arrangement freed up the extra space needed by the bulky autoland equipment positioned beneath the cockpit. The main gear had quad-wheel bogies with wheels arranged side-by-side and were fitted with Hawker Siddeley shock absorbers. They rotated 90 degrees and increased six inches in length during retraction into the under-fuselage centre section wells. Wheels were supplied by Hoffar's Automobile Division built to a Dunlop design with tyres from Dunlop, fitted with multiple disc brakes with the Dunlop Maxaret anti-skid system. An optional gravel kit was available to allow the Trident 7A to land on unprepared strips; this was made available for all subsequent DHBC Tridents.
Cabin pressurisation and air conditioning was achieved by means of two Hawker Siddeley Dynamics aircon systems, of which only one was needed for complete cabin pressurisation. The aft section, the undercarriage wells, and the wing centre section were unpressurised. A pneumatic system was installed for lavatory water and toilet flushing.
Baggage, cargo, and mail were carried in two below-decks holds fore and aft of the wing, accessed via a single hatch for each located starboard; like the main doors, they were of plug type. An optional aircon system was available to allow for the transport of live animals in the forward hold.
The first prototype Trident 7A (c/n C826/1966), registered VB-TRI, was completed in March 1966 and made its maiden flight on 11 April; two more were completed in May (VB-TRJ, c/n C835/1966) and June (VB-TRK, c/n C843/1966). TRK was written off after a landing accident following a test flight, but the other two prototypes were converted to a Combi configuration and transferred to the Royal BC Air Force in 1970, which operated them until 1992; the first prototype is preserved at RBCAF Kelowna.
Production of the Trident 7A had begun on the basis of a firm order for 25 from Inter-Dominion placed in 1965, followed a month later by an order for nine from Air BC; but a major coup came shortly afterwards, when Southern Airways of the US placed an order for fourteen. Two other American airlines placed orders for the Trident 7A, Pacific Southwest Airlines for five and Panagra Airways for eight, a total of twelve were sold to Brazil - six each to VARIG and Cruzeiro do Sul, and five went to Air Jamaica of the West Indies, but only eight were sold outside of the Americas, to All Nippon Airways of Japan. Pacific Western Airlines (twelve), Awyr Cymru Newydd (two), and the Royal BC Air Force (three) were the other three customers. Including the prototypes a total of 105 Trident 7A were built between 1966 and 1973; the last one (c/n C1322/1973) was delivered to Panagra Airways.
Five remain in service as of 2022, of which three are with Aerosucre Colombia; these had been converted to freighters in 2000. The other two - both having been converted to Combi configuration, are in Angola, one with Air Gemini and the other owned by Transafrik International and operated on behalf of TAAG Angola Airlines.
(to be continued...)
