de Havilland Canada Dash 7
|Dash 7 in Voyageur Airways colours at the Winnipeg International Airport, 2005.|
|Type||Regional STOL airliner|
|Manufacturer||de Havilland Canada|
|Maiden flight||27 March 1975|
|Introduced||3 February 1978|
|Primary users||Various airlines|
United States Army
|Developed from||DHC-6 Twin Otter|
|Variants||de Havilland Canada Dash 8|
The de Havilland Canada DHC-7, popularly known as the Dash 7, is a turboprop-powered regional airliner with STOL capabilities. It first flew in 1975 and remained in production until 1988 when the parent company, de Havilland Canada, was purchased by Boeing.
Design and development
In the 1960s, de Havilland Canada was already well known worldwide for their series of high-performance STOL aircraft, notably the very popular Twin Otter. However, these aircraft were generally fairly small and served outlying routes, as opposed to the main feederliner routes which were already well served by larger, higher-performance aircraft such as the Handley Page Jetstream and Fokker F27.
The de Havilland Canada company felt they could compete with these designs in a roundabout way. With their excellent STOL performance, their designs could fly into smaller airports more centrally located in city centers, with runways that the other aircraft could not easily use. The original specification called for a 40-passenger aircraft with a fairly short range of 200 statute miles, operating from runways only 2,000 ft long.
With new noise restrictions coming into effect throughout the 1970s, an aircraft tailored for this role would also have to be very quiet. To meet this restriction, the new design used oversized propellers geared to spin at a slower speed than normal; much of the sound from a propeller is generated at the tips which are spinning near the speed of sound, and therefore, by reducing the number of RPM, this noise is reduced substantially. The Dash 7 often landed with only 900 RPM, and took off at only 1,200.
In other respects, the new DHC-7 was essentially a larger, four-engine version of the Twin Otter. The general layout remained similar, with a large T-tail intended to keep the elevator clear of the propwash during takeoff, a high aspect ratio high-mounted wing, and most details of the cockpit and nose profile. Changes included the addition of cabin pressurization which required a switch to a fuselage with a circular cross-section and landing gear that folded forward into the inner engine nacelles.
Most of the rear wing was spanned by a complex double Fowler flap arrangement for high low-speed lift. The Twin Otter also included "flapperons" that drooped the ailerons as part of the flaps, but these were removed due to safety concerns. Instead the ailerons were reduced in size to allow more flap area, and were so small that they had to be aided by spoilers. On touchdown, hydraulic pressure was automatically reduced in the flaps, allowing them to "blow back" to the 25% position and thus "drop" the aircraft to the runway for better braking performance. The flaps would also "blow back" when engine power was increased during a go-around. The four-engine layout aided lift at low speeds due to the wide span of the propellers blowing air over the wing. When reverse thrust was selected on landing, the props "stole" airflow from the wing, further decreasing lift and increasing the effectiveness of the brakes. More importantly, if an engine failed, the asymmetric thrust was much less than on a twin-engine layout, thereby increasing safety and allowing for a lower minimum control speed with an engine inoperative (Vmc). The engines could actually produce drag in flight at idle speed, allowing fine control of the glide slope.
Development started in 1972 and the prototype first flew on 27 March 1975. Testing went smoothly, and the first delivery took place to Rocky Mountain Airways on 3 February 1978. One hundred were delivered by 1984, when the production line was put on hold in favour of the Dash 8. Another 13 were delivered between 1984 and 1988, when the production lines were removed when Boeing bought the company.
The original Series 100 represents the vast majority of the aircraft delivered, and came in two models; the -102 passenger version and -103 combi with an enlarged cargo door. These were followed by the Series 110 which met British CAA requirements, including the -110 and -111, and finally the Series 150 which included additional fuel tankage and an improved interior in the -150 and -151. There were plans for a Series 200 with the new PT6A-50/7 engines which improved hot-and-high power, but these plans were shelved when Boeing ended production of the design.
The mixture of features on the Dash 7 met with limited commercial success. Most turboprop operators used them as feederliners into large airports, where the STOL performance wasn't considered important. In comparison to other feederliners, the Dash 7's four engines required twice the maintenance of a twin-engine model, thereby driving up operational costs. Finally, those airports that did require a high performance STOL operation were generally small and well served by the Twin Otters; had the airport needed a larger plane to serve its customer base, they would have built larger runways. One exception to this was operations at London City Airport which, upon opening in 1987, was capable of handling few aircraft types besides the Dash 7.
The executives at de Havilland realized they had simply misread the market and ended production in 1988.  Learning from their mistakes, de Havilland started the design of a much more "conventional" twin-engine design in 1978, the extremely popular Dash 8. The DHC-7 production line eventually delivered 113, of which four have been lost and one scrapped. Many of the rest remain in service.
In August 2006, a total of 71 Dash 7 aircraft (all variants) remain in airline service. Major operators include:
- Air Greenland (6)
- Arkia Israel Airlines (5, only 2 active for passenger flights )
- Asian Spirit (6)
- Berjaya Air (4)
- Pelita Air Service (6)
- Petroleum Air Services (5)
- Travira Air (1)
- Voyageur Airways (6)
- Air Tindi (3)
- Aerovías DAP (1)
Some ten other airlines operate small numbers of the aircraft.
Other civilian operators
The British Antarctic Survey (BAS) operates a single Dash-7 in support of its research program in Antarctica. The aircraft undertakes regular shuttle flights between either Stanley on the Falkland Islands, or Punta Arenas in Chile, and the Rothera Research Station on Adelaide Island. It also operates to and from the ice runway at the Sky Blu Logistics Facility on the Antarctic mainland.
- United States Army (10)
Incidents and accidents
The de Havilland Canada DHC-7 has been involved in six accidents with a total of 68 fatalities.
- Crew: 2
- Length: 80 ft 7¾ in (24.58 m)
- Wingspan: 93 ft 0 in (28.35 m)
- Height: 26 ft 2 in (7.98 m)
- Wing area: 860 ft² (80 m²)
- Empty weight: 27,650 lb (12,540 kg)
- Max takeoff weight: 44,000 lb (20,000 kg)
- Powerplant: 4× Pratt & Whitney Canada PT6A-50 turboprops, 1,120 shp (835 kW) each
- Maximum speed: 235 knots (271 mph, 436 km/h)
- Range: 700 nm (770 mi, 1,400 km)
- Service ceiling: 21,000 ft (6,400 m)
- Hotson, Fred W. The De Havilland Canada Story. Toronto: CANAV Books, 1983. ISBN 0-07-549483-3.
- Canadian Forces:
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