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DHC-6 Twin Otter
A West Coast Air Twin Otter floatplane.
Type	utility aircraft
Manufacturer	de Havilland Canada
Designed by	Fred Buller and Dick Hiscocks
Maiden flight	20 May 1965
Introduced	1968
Produced	1965-1988
Number built	844
Variants	de Havilland Canada Dash 7

The DHC-6 Twin Otter is a 20-passenger STOL (Short Takeoff and Landing) utility aircraft developed by de Havilland Canada. It has often been called the most successful aircraft program in Canada's history. The aircraft's fixed tricycle undercarriage, STOL abilities and relatively high rate of climb have made it a successful cargo, regional passenger airliner and MEDEVAC aircraft. In addition, the Twin Otter has been popular with commercial skydiving operations. It is generally limited to carrying 19 jumpers (a relatively large load compared to most other aircraft in the industry); presently, the Twin Otter is used in skydiving operations in Sweden, Finland, Norway, Spain, Australia, Canada, the USA and other nations worldwide.

Development of the aircraft began in 1964, with the first flight on 20 May 1965. A twin-engined replacement for the Otter had been planned by de Havilland Canada. Twin engines not only provided improved safety but also allowed for an increase in payload while retaining the renowned STOL qualities. Design features included double slotted trailing edge flaps and ailerons that work in unison with the flaps to boost STOL performance. The availability of the 550 shp Pratt and Whitney Canada PT6A-20 propeller turbine engine in the early 1960s made the concept of a twin more feasible. To bush operators, the enhanced reliability of turboprop power and the enhanced performance of a twin-engined configuration made it an immediately popular alternative to the single engine, piston-powered Otter which had been flying since 1951.

de Havilland Twin Otter in British Airways Livery taking off from Barra Airport in the Summer of 2004

The first six aircraft produced were designated Series 1, indicating that they were prototype aircraft. The initial production run consisted of Series 100 aircraft, serial number seven to 115 inclusive. In 1968, Series 200 production began with serial number 116. Changes made at the beginning of Series 200 production included improving the STOL performance, adding a longer nose that was equipped with a larger baggage compartment (except to aircraft fitted with floats) and fitting a larger door to the rear baggage compartment. All Series 1, 100, and 200 aircraft and their variants (110, 210) were fitted with the 550 shaft horsepower PT6A-20 engines.

In 1969, the 300 series was introduced, beginning with serial number 231. Both aircraft performance and payload were improved by fitting more powerful PT6A-27 engines. This was a 680 hp engine that was flat-rated to 620 hp for use in the Series 300 Twin Otter. The Series 300 proved to be the most successful variant by far, with 614 Series 300 aircraft and their sub-variants (Series 310 for United Kingdom operators, Series 320 for Australian operators, etc.) sold before production ended in 1988.

Twin Otter taking off from a gravel airstrip near Sila Lodge at Wager Bay (Ukkusiksalik National Park, Nunavut, Canada)

de Havilland Canada DHC-6 Twin Otter on Beechey Island at seamen graves of John Franklin expedition (Nunavut, Canada) c. 1997. Note the "tundra tyres."

Twin Otters could be delivered directly from the factory with floats, skis or tricycle landing gear fittings, making them adaptable bush planes for remote and northern areas including Canada and the United States, specifically Alaska. Many Twin Otters still serve in the far north, but they can also be found in Africa, Australia, Antarctica and other regions where bush planes are the optimum means of travel. Their versatility and maneuverability have made them popular in areas with difficult flying environments, including Papua New Guinea. In Norway, the Twin Otter paved the way for the network of short-field airports, connecting the rural areas with the larger towns with outstanding reliability, and remained in service until 2000 on certain routes. Widerøe of Norway was, at one time, the world's largest operator of Twin Otters. During one period of its tenure in Norway, the Twin Otter fleet achieved over 96,000 cycles (takeoff, flight and landing) per year.

Twin Otters, rated for flight down to −75°C (−103°F),^[1] are a staple of Antarctic transportation. On April 24–25, 2001, two Twin Otters performed the only winter flight to Amundsen-Scott South Pole Station to perform a medical evacuation.^[2][3][4]

As of August 2006, a total of 584 Twin Otter aircraft (all variants) remain in service worldwide. Major operators include: Libyan Arab Airlines (16), Maldivian Air Taxi (17), Trans Maldivian Airways (15), Kenn Borek Air (17) and Scenic Airlines (11). Some 115 airlines operate smaller numbers of the aircraft including the British Airways subsidiary airline, Loganair.

Ontario's Ministry of Natural Resources is also a long-time operator of the Otter.

The United States Air Force operates three Twin Otters for the United States Air Force Academy's skydiving team. The cadets affectionately call the aircraft the "'Twotter."

After series production ended, the remaining tooling was purchased by Viking Air of Victoria which manufactures replacement parts for all of the out of production de Havilland Canada aircraft. On 24 February 2006, Viking purchased the type certificates from Bombardier Aerospace for all the out of production de Havilland DHC-1 through DHC-7 aircraft.^[5] The ownership of the certificates gives Viking the exclusive right to manufacture new aircraft.

On 17 July 2006, at the Farnborough Air Show, Viking Air announced its intention to offer a "Series 400" Twin Otter.^[6] Restarting the production would be dependent on the ability to realize enough initial orders.

In April 2007, Viking announced that it would restart production of the Twin Otter with a more powerful PT6A-34/35 engine.^[7] At the time, Viking had 27 orders and options in hand. As of November 2007, 40 firm orders and 10 options have been taken and a new assembly plant has been established in Calgary, Alberta with production tentatively scheduled to start in January 2008.^[8] The parts are made in Victoria, British Columbia then shipped to Calgary, Alberta for assembly.

DHC-6 Series 100 

Twin-engined STOL utility transport aircraft, powered by two 432-kW (550-shp) Pratt & Whitney Canada PT6A20 turboprop engines.

DHC-6 Series 200 

Improved version.

DHC-6 Series 300 

Twin-engined STOL utility transport aircraft, powered by two 620-shp (462-kW) Pratt & Whitney Canada PT6A-27 turboprop engines.

DHC-6 Series 300M 

Multi-role military transport aircraft. Two of these were produced as 'proof of concept' demonstrators

DHC-6 Series 300MR 

Maritime reconnaissance version.

DHC-6 Series 300S 

Six demonstrator aircraft fitted with 11 seats, wing spoilers and an anti-skid braking system.

CC-138 

Twin-engined STOL utility transport, search and rescue aircraft for the Canadian Forces.

UV-18A 

Twin-engined STOL utility transport aircraft for the US Army Alaska National Guard. Six built. It has been replaced by the C-23 Sherpa in US Army service.

UV-18B 

Parachute training aircraft for the United States Air Force Academy. The United States Air Force Academy's 98th Flying Training Squadron maintains three^{[citation needed]} UV-18s in its inventory as freefall parachuting training aircraft, and by the Academy Parachute Team, the Wings of Blue, for year-round parachuting operations.

• 2007 Air Moorea DHC-6 Twin Otter crash killed all passengers and crew.

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General characteristics

• Crew: Minimum one, commonly two. (A flight attendant must be on board if there are more than 19 passengers)
• Capacity: 19 or 20 passengers
• Length: 51 ft 9 in (15.77 m)
• Wingspan: 65 ft (19.8 m)
• Height: 19 ft 6 in (5.9 m)
• Wing area: 420 ft² (39 m²)
• Empty weight: between 7,000 lb (3,363 kg) and 8,000 lb (3,628 kg)
• Max takeoff weight: 12,500 lb (5,670 kg)
• Powerplant: 2× Pratt & Whitney PT6A-27 turboprop engines, 620 hp - 680 hp (460 kW - 507 kW) each

Performance

• Maximum speed: 183 knots (210 mph, 338 km/h)
• Range: 920 nautical miles (1,050 mi, 1,705 km)
• Service ceiling: 26,700 ft (8,140 m)
• Rate of climb: 1600 ft/min (8.1 m/s)

Notes

Bibliography

• Bush planes

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Designation sequence

DHC-3 - DHC-4 - DHC-5 - DHC-6 - DHC-7 - DHC-8