| Avro 748 | |
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| Avro 748 (C-GBFA) registered to First Air at Cambridge Bay Airport, Nunavut, Canada. | |
| Type | airliner |
| Manufacturer | Avro |
| Maiden flight | June 24 1960 |
| Primary users | Indian Air Force Indian Airlines Corporation |
| Number built | 380 |
| Developed from | Hawker Siddeley Andover |
| Variants | BAe ATP |
The Avro 748 was a small short-range turboprop airliner designed by Avro in the late 1950s as a replacement for the now-aged DC-3's then in widespread service as feederliners. Avro concentrated on performance, notably for STOL operations, and found a dedicated market and 380 aircraft were built. A larger development, the BAe ATP, attempted to compete with the de Havilland Canada Dash 8 but saw a limited production run.
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Development
The original 748 design started in 1958 after the infamous Duncan Sandys 1957 Defence White Paper ended most military manned aircraft development in the UK, and Avro decided to re-enter the civilian market. The Vickers Viscount had the large end of the short-haul market neatly wrapped up, so Avro decided to design to a smaller feederliner design to replace the many DC-3 Dakotas that were now reaching the end of their lifespan. Avro was not the only company to see the potential for a DC-3 replacement, and by this point the Fokker F27 Friendship was well advanced. Avro decided to compete by producing a design with better short-field performance, allowing it to operate from smaller airports. The first aircraft flew from Avro's Woodford plant on June 24 1960, and two prototypes quickly proved the type's short field performance. Eighteen 748 Series 1 aircraft were produced, the first for British Skyways Coach-Air (later known as Dan-Air) but the majority for Aerolíneas Argentinas. By this point Avro's individual identity within the Hawker-Siddeley Group had ended and the design was known as the HS 748. The Series 2 entered production in 1961 with a higher take-off weight, and were produced to 198 examples, making it one of the most popular post-war British designs. The more powerful Series 2A followed for another 71, along with another 25 Series 2Bs. The Royal Air Force ordered a version (as the Hawker Siddeley Andover C1) modified with a raised tailplane to accommodate a rear loading ramp and a kneeling undercarriage. The 748 Series 1 and Series 2 was license produced in India by Hindustan Aeronautics as the HAL-748. HAL built 89 aircraft in India, 72 for the Indian Air Force and 17 for the Indian Airlines Corporation. The later production for the Indian Air Force (the last 20 built) were Series 2M aircraft with a Large Freight Door. Aircraft were later modified for a variety of roles including a trials aircraft for an Airborne Early Warning version fitted with a large radome. Hawker Siddeley became part of British Aerospace in the mid-1970s with the Series 2B becoming the main production model. The last 748s were built as "Super 748s" with hush-kitted Rolls-Royce Dart engines, in 1987. Two other versions were the Coastguarder and Super 748. The Coastguarder was a maritime patrol version. The ICAO designator as used in flight plans is A748.
Mishaps
There have been 19 crashes of the HS-748. One of the better known and most thoroughly investigated accidents was the crash of an Air Illinois HS 748 on October 11, 1983. It is the only crash of a HS 748 in the United States. While cruising at night, the aircraft's no.1 generator failed and the crew mistakenly shut down the no.2 generator. After repeated attempts to reset it failed, the Captain made the decision to continue the flight, despite knowledge that the batteries could only provide 30 minutes of power. After 29 minutes, the aircraft lost all electrical power and crashed into a field. Subsequent investigation revealed a long chain of events that led up to the failure. The first one was the overhaul of the number 1 generator. The original aramature had been built with metal wire windings used as clamps on the ends. During the overhaul (done in the USA) the wound clamps were replaced with metal straps (standard on American made units). These straps were not as heat tolerant and would prove insufficient for the British made generator armatures. Regardless of this the unit was issued a "yellow tag" and returned to service. Second was the repeated "tripping off" of the number 2 generator. The number 2 generator had been tripping off on a fairly regular basis during high electrical demand situations such landing gear retraction. The crew had become used to resetting it. Third was the short taxi at the departure airport. The crew had left the battery on while they went in to check the weather for the next flight. This allowed the flight attendant and 4 passengers to have light and power on the brief stop but ran the NiCad battery down. The subsequent short taxi did not allow the battery time to properly recharge. This allowed the battery to "knee-cap" or have a sudden loss of power 29 minutes after generator loss. Fourth was the weather. Had it been VFR (visual flight rules: good visibility) this accident would likely have been avoided. This night was IFR (instrument flight rules: poor visibility and weather conditions). Sadly, VFR conditions existed only about 10 minutes further down the proposed flight route. Fifth, and perhaps most important, was the cockpit crew. The plane took off at night in poor weather conditions with a partially charged battery, one generator with a propensity to trip off and the other (unknown to the crew) about to have a major failure. At gear retraction the number 1 generator failed completely. The flight crew, used to resetting the cantankerous number 2 generator, tried to reset it again. This time it was actually the working generator. When the number 2 generator was taken off line during the reset attempt, the weak battery became the plane's sole source of electricity. At this time the crew should have returned to the airport. The decision to press one was a fatal one. They were never able to get the number 2 generator back on line and the number 1 generator was completely inoperative. Apparently the heat it generated finally weakened the generator's armature binding straps to the point of failure and the armature failed completely. The crew were in low visibility at night and were completely dependant on their flight instruments. When the battery failed they were down to flying on flashlights. There was considerable confusion in the cockpit by now and the crew were trying to remember which flight instruments were electrically driven and which were vacuum driven (the vacuum driven still being reliable). The aircraft departed level flight and the crew fell victim to vertigo. The aircraft hit the ground at over 300 knots, nose low in a steep bank killing all 7 occupants.
Operators
Civil operators
In August 2007 a total of 59 Avro 748 aircraft (all variants) remain in airline service. Current operators are[1]:
- Best Air (2)
- Bismillah Airlines (1)
- Z Airways (1)
'
Canada
- Air Creebec (4)
- Air Inuit (4)
- Air North (4)
- Calm Air (6)
- First Air (3)
- Wasaya Airways (5)
- International Trans Air Business (1)
- Trans Service Airlift (2)
- Comores Aviation (2)
- Guinee Air Cargo (1)
- 748 Air Service (1)
- African Commuter Services (1)
- Executive Aerospace (5)
- Stars Away Aviation (2)
- Aero Lanka (1)
- West Air Sweden (1)
Military operators
- Royal Australian Air Force
- School of Air Navigation RAAF/No. 32 Squadron RAAF
- No. 34 Squadron RAAF
- Fleet Air Arm (RAN)
- No. 723 Squadron RAN
- No. 851 Squadron RAN
Specifications (Super 748)
Data from Jane's Civil and Military Aircraft Upgrades, 1994-95[2]
General characteristics
- Crew: Three (two pilots + one passenger attendant)
- Capacity: 40-58 passengers
- Payload: 5,136 kg (11,323 lb)
- Length: 20.42 m (67 ft 0 in)
- Wingspan: 31.23 m (102 ft 5½ in)
- Height: 7.57 m (24 ft 10 in)
- Wing area: 77 m² (829 m²)
- Empty weight: 12,327 kg (27,126 lb)
- Max takeoff weight: 21,092 kg (46,500 lb)
- Powerplant: 2× Rolls-Royce Dart RDa.7 Mk 536-2 turboprop, 1,700 kW (2,280 ehp) each
Performance
- Cruise speed: 452 km/h (244 knots, 281 mph)
- Range: 1,715 km (926 nm, 1,066 mi) (with max payload)
- Service ceiling 7,620 m (25,000 ft)
- Wing loading: 274 kg/m² (56.1 lb/ft²)
- Power/mass: 0.161 kW/kg (0.0981 hp/lb)
References
- ^ Flight International, 21-27 October 2007
- ^ Michell, Simon (editor) (1994). Jane's Civil and Military Aircraft Upgrades, 1994-95. Jane's Information Group. ISBN 0 7106 1208 7.
External links
Related content
Related development
Comparable aircraft
Designation sequence
- 696 - 698 - 707 - Avro Ashton - 748
See also
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| General | Timeline of aviation · Aircraft · Aircraft manufacturers · Aircraft engines · Aircraft engine manufacturers · Airports · Airlines |
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| Notable incidents and accidents | Military aviation · Airliners · General aviation · Famous aviation-related deaths |
| Records | Flight airspeed record · Flight distance record · Flight altitude record · Flight endurance record · Most produced aircraft |
