The Hawker Siddeley HS 748 is a medium-sized turboprop airliner originally designed and initially produced by the British aircraft manufacturer Avro. It was the last aircraft to be developed by Avro prior to its absorption into Hawker Siddeley.
The HS 748 was developed during the late 1950s as a move to re-orient the company towards the civil and export markets. Powered by the popular Rolls-Royce Dart turboprop engine, it was specifically designed as a modern feederliner to act as a replacement for the aging Douglas DC-3s then in widespread service. Originally intended to seat a smaller number of passengers, market research indicated that a seating capacity of around 40 passengers would be optimal for the type. As a means to differentiate the new airliner from competitors, it was designed to possess a high level of performance, including its short takeoff and landing (STOL) capabilities and overall ruggedness. First flying on 24 June 1960, the series 1 HS 748 entered revenue service in 1961.
Once in service, the HS 748 found itself a niche within the short-haul market. Several different models would be developed of the regional airliner, typical improvements being the adoption of increasingly powerful Dart engines and a higher gross weight. Perhaps the most distinct variant was the HS 780 Andover, a dedicated military transport model developed for the Royal Air Force (RAF) that featured a large rear loading ramp and a squatting main landing gear to assist in loading bulky freight items.
By 1988, the year in which production of the type was terminated, 380 aircraft had been produced between Hawker Siddeley (the owning company of Avro) and Indian aviation company Hindustan Aeronautics Limited (HAL). During the 1990s, a larger, stretched development of the HS 748, the BAe ATP, was developed and had attempted to compete with market leaders such as the de Havilland Canada Dash 8 and ATR 42, but saw only limited sales prior to production being terminated.
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 manned 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 upon 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.
Early intentions for 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.