Hawker Siddeley HS 748

The Hawker Siddeley HS 748 (formerly Avro 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.
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.
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.
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. From 1971 onwards, several new options were made available to customers, including a large freight door in the rear cabin and a strengthened cabin floor. During 1979, the Series 2B was introduced, which saw a 4-foot increase in wingspan, the adoption of Mk 536-2 engines, along with a modernised passenger cabin, and various improvements to the fuel, water methanol injection system, and engine fire protection systems.
During 1976, Eric Johnson, sales engineering manager of Hawker Siddeley Manchester, stated that the company was studying options for equipping a model of the HS 748 with turbofan engines, and that a preferred powerplant at that point was the Rolls-Royce/SNECMA M45H, as used on the VFW-Fokker 614 jetliner. Other changes would likely have been incorporated, including the addition of lift dumpers and adaptive brakes for better landing performance, while electrical, hydraulic and air conditioning systems would be redesigned; externally, a dihedral would have to be introduced to keep the tailplane clear of the jet exhaust. It was envisioned that the reengined aircraft could offer larger seating arrangements of up to 64 seats.
In addition to the British production line, manufacture of the 748 was also performed overseas. Early on, India had placed orders for the type. Both the 748 Series 1 and Series 2 were licence-produced by Indian manufacturer Hindustan Aeronautics (HAL), aircraft produced by the company were designated HAL-748. On 1 November 1961, the first Indian-assembled HAL-748 made its initial flight. By the end of production, HAL had completed 89 Indian-built aircraft, 72 of which were for the Indian Air Force and 17 were delivered to national flag carrier Indian Airlines.
While the HS 748 was originally intended to be marketed principally towards the civilian market, numerous examples were sold to military customers around the world. Hawker Siddeley used the design as the basis for the HS 780 Andover, a military transport aircraft developed and produced for the Royal Air Force. In terms of its design, the HS 780 was broadly similar to the 748, differing primarily by its redesigned rear fuselage and empennage, which incorporated a large rear loading ramp and a squatting main landing gear to better facilitate the loading of bulky freight items. The 780 also used the more powerful RDa.10/1 3,245 hp (2,419.80 kW) estimated power at 15,000 rpm, with Water/Methanol injection
During 1988, production of the HS 748 was terminated, while the last British-assembled aircraft made its first flight on 1 December of that year. BAE then started producing a product improved, stretched version the BAE ATP 61 which uses the PWC 126/127 engines. Total production of this variant was only 67 aircraft. According to BAE Systems, a successor company to Hawker Siddeley, during the type's production life, a total of 381 aircraft had been produced, which included both the Andover and HAL-built examples.
Within its first decade of its availability, sales of the HS 748 had reportedly been relatively brisk; by 1976, the sale of 312 aircraft had been recorded, of which 259 had been to export customers. Within ten years of its launch, India had emerged as the largest single market for the airliner, Indian Airlines being the largest HS 748 operator with a fleet of 26 aircraft. It had been popular with numerous commercial operators; across the Caribbean and Latin America alone, 63 HS 748s were in operation with 11 separate operators.
The HS 748 had been able to achieve some triumphs over competing rivals, including the F27 Friendship. Philippine Airlines had been the F27's largest operator prior to its decision to replace both it and its remaining DC-3s with the HS 748, which represented a significant sales coup for Hawker-Siddeley. Other major civil operators included Aerolíneas Argentinas, VARIG, Thai Airways, LAN-Chile, and Bouraq Airlines. Several of these operators would utilise its STOL capabilities in their services; according to Flight International, over one-third of all scheduled operations reportedly involved operations from rough airstrips with minimalist facilities.
Another key market for the HS 748 was the executive role; the type was repeatedly procured to serve as the designated aircraft for various heads of state, including those of Argentina, Brazil, Chile, India, Venezuela, Zambia, Thailand and the United Kingdom. The HS 748 was one of the last planes to be flown by noted aviator and business magnate Howard Hughes. During 1972, Hughes performed several flights of the type, each time accompanied by Hawker Siddeley test pilot Tony Blackman, flying from the company's airport in Hatfield, Hertfordshire.
The Australian military purchased several aircraft; specifically, the Royal Australian Air Force (RAAF) procured a fleet of ten HS 748s, the first of which arrived in 1968 for navigation training and transporting VIPs. The Royal Australian Navy (RAN) operated a pair of HS 748s starting in 1973 as a navigational trainer. Following Cyclone Tracy, relief aid was delivered across Darwin, Northern Territory, using the type; after being fitted with various electronic countermeasures (ECM) during the late 1970s, HS 748s were also used for electronic warfare training.
In a typical passenger configuration, the HS 748 can accommodate around 40–48 economy class seats in a four abreast layout; however, the majority of later-serving passenger HS 748s were typically operated as quick change combis. These aircraft are fitted with a movable bulkhead that divides the main cabin, housing between 4 and 40 seats in the rear section while cargo is placed in the forward section. The 748 has also been widely used as a pure freighter, having a typical maximum payload of about 12,000 lbs. Several carriers have used the 748 as a bulk fuel hauler, in which capacity it is normally with either seven or eight fixed tanks in the cabin, possessing a total capacity of about 7,500 L (1,600 imp gal; 2,000 US gal).
The ICAO designator as used in flight plans is A748.
As of July 2020, a total of 13 HS 748 aircraft (all variants) remained in airline service. As of May 2023, Transport Canada (TC) listed 7 HS 748 in Canada with a current Certificate of Registration.
Current operators are:
Data from Jane's Civil and Military Aircraft Upgrades, 1994–95, BAE Systems
General characteristics
Performance
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