Hawker Siddeley HS 748

Development

Background

Following the release of the 1957 Defence White Paper, in which then-Minister of Defence Duncan Sandys announced the termination of almost all crewed military aircraft development, aircraft manufacturer Avro decided that it should place a greater emphasis upon the civilian market. Ten years prior, it had launched a civilian airliner, the Avro Tudor series, but this had encountered few sales; thus, during 1958, it was decided to commence work on a clean-sheet design, which would eventually become the HS 748. On 9 January 1959, the existence of the project, then referred to as the Avro 748, was announced to the public.

By this point, the four-engined Vickers Viscount had already secured the larger end of the short-haul market; therefore, Avro decided that it would design a smaller regional airliner, powered by a pair of Rolls-Royce Dart turboprop engines. It was envisioned that this aircraft would be a suitable replacement for the many DC-3 Dakotas that were by then reaching the end of their economic lifespan. According to aviation periodical Flight International, a major goal for the design team was to produce an aircraft that would be capable of operating from any airfield from which the DC-3 could be operated.

Initially, the airliner was planned to be a 20–30 seat aircraft, adopting a somewhat similar configuration to the future rival Fokker F27 Friendship; however, following discussions with several potential customers, the company opted for a low-wing 40-seat configuration. It was this latter arrangement that was chosen for the 748 project. Another important focus for the prospective airliner was compliance with both British and American standards of airworthiness; accordingly, it would be one of the first medium-sized aircraft to incorporate fail-safe design principles for its structure in place of the then-common safe-life principles being practiced. The airframe effectively lacked any imposed lifespan; during development, it was successfully tested using a water tank for up to the equivalent of 100,000 flight hours.

Avro was not the only company to see the potential for a DC-3 replacement and, by this point, work on the 748's direct competitor, the Dutch-built F27 Friendship, was well advanced. To differentiate itself from the competition, Avro decided to focus its efforts upon achieving a more rugged design that offered superior short takeoff and landing (STOL) performance, which enabled the prospective airliner to be operated from smaller and more austere airports, including those without modern runways. This STOL capability was accomplished via several features, including the adoption of a long, high lift wing, which was fitted with a unique single slot flap with a hinged flap tab at the trailing edge. This wing was mounted low on the fuselage with dihedral from the root, allowing for good overall ground clearance and the easy mounting of strong landing gear. Operationally, pilots were provided with a choice of three takeoff flap settings to select the level of STOL performance required.

Another supportive feature of the 748 was a design decision to adopt straightforward systems and use proven components where realistically possible. For operator convenience, the engines were provided with an internal ignition system; various other systems and structures throughout the airliner were designed to be easy to inspect and to perform repairs upon, even when at unprepared airstrips with limited equipment available. Likely as a consequence of these favourable qualities, the 748 quickly attracted the attention of a variety of airlines, particularly those that typically operated in remote areas, which has been attributed to its ability to operate from short, rough fields without any ground service equipment while being capable of hauling payloads in excess of 10,000 lb.

Into flight

On 24 June 1960, the first Avro 748 made its maiden flight from the company's Woodford, Cheshire, aircraft factory. Flight testing of the two prototypes quickly validated the type's short-field performance. Eighteen Avro 748 Series 1 aircraft were produced; during April 1962, the first production aircraft were delivered to launch customer Skyways Coach-Air Limited. However, the majority of the series 1 were export sales to operator Aerolíneas Argentinas. During the early 1960s, Avro's individual identity within the Hawker Siddeley Group was expunged, after which the airliner was marketed by the parent company as the HS 748.

After the initial batch of series 1 aircraft was completed, production transitioned to the improved series 2. The series 2 was largely similar to its predecessor, principally benefiting from the adoption of more powerful Dart RDa 7 Mk 531 engines and an increased gross weight. According to aviation periodical Flight International, during 1960, the basic price for a new Avro 748 Series 1 was £176,000, while that of the corresponding Avro 748 Series 2 was reportedly £196,000.

During 1967, the series 2A was introduced, which was the same basic aircraft powered by Mk. 532 engines along with a further increase in gross weight.