de Havilland Canada DHC-6 Twin Otter

DHC-6 Twin Otter
	A West Coast Air DHC-6 Twin Otter floatplane.
Role	utility aircraft
Manufacturer	de Havilland Canada, Toronto ON ; Viking Air - (400 series), Victoria BC
First flight	May 20, 1965
Introduction	1966
Produced	1965–1988; 2008–present
Number built	846
Developed from	DHC-3 Otter
Developed into	de Havilland Canada Dash 7

The DHC-6 Twin Otter is a Canadian 19-passenger STOL (Short Takeoff and Landing) utility aircraft developed by de Havilland Canada and currently produced by Viking Air. The aircraft's fixed tricycle undercarriage, STOL abilities and 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, and it is used by the United States Army Parachute Team.

Design and development

Development of the aircraft began in 1964, with the first flight on May 20, 1965. A twin-engined replacement for the single-engined 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 (410 kW) 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 improved reliability of turboprop power and the improved 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.

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 Series 300 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 (510 kW) engine that was flat-rated to 620 hp (460 kW) 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.

New production

After Series 300 production ended, the remaining tooling was purchased by Viking Air of Victoria, British Columbia, who manufacture replacement parts for all of the out of production de Havilland Canada aircraft. On February 24, 2006 Viking purchased the type certificates from Bombardier Aerospace for all the out of production de Havilland DHC-1 through DHC-7 aircraft.^[1] The ownership of the certificates gives Viking the exclusive right to manufacture new aircraft.

On July 17, 2006, at the Farnborough Air Show, Viking Air announced its intention to offer a Series 400 Twin Otter. On April 2, 2007 Viking announced that with 27 orders and options in hand, it was restarting production of the Twin Otter, equipped with a more powerful Pratt & Whitney Canada PT6A-34/35 engine.^[2] As of November 2007, 40 firm orders and 10 options had been taken and a new assembly plant established in Calgary, Alberta.^[3]^[4] Zimex Aviation of Switzerland received the first new production aircraft, serial number 845, in July 2010.^[5]^[6]

Major changes introduced with the Series 400 include Honeywell Primus Apex fully integrated avionics, deletion of the AC electrical system, deletion of the beta backup system, modernization of the electrical and lighting system, and use of composites for non-load-bearing structures such as doors.^[7]

Announced orders

Peruvian Air Force (12)
Air Loyaute (2)
Air Moorea (2)^[4]
Air Seychelles (2)^[4]
Airfast Indonesia (4)^[8]
European Coastal Airlines (6)
Global Aerospace Logistics (GAL) (10), Order placed June 16, 2009
Loch Ard Otters (6 plus 6 options)^[4]
Montenegro Charter Company (1)^[9]
Maldivian Air Taxi (2)
Petro Air (1)
Trans Maldivian Airways (5)^[4]
United States Army Parachute Team (3)^[10]
Vityaz Avia Corporation (2)
Zimex Aviation (1)^[4]

Possible international Twin Otter production

Over the decades several organizations were interested in production of the versatile DHC-6 Twin Otter, the rights to which were acquired in 2006, with several other de Havilland Type Certificates, by Viking Air of Victoria, British Columbia. In February 2011, PT Dirgantara Indonesia of Indonesia discussed the possibility of Twin Otter production at their facilities.^[11]^[12]

Operational history

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 are a staple of Antarctic transportation.^[13] Four Twin Otters are employed by the British Antarctic Survey on research and supply flights, and several are employed by the United States Antarctic Program via contract with Kenn Borek Air. On April 24–25, 2001, two Twin Otters performed the only winter flight to Amundsen-Scott South Pole Station to perform a medical evacuation.^[14]^[15]^[16]^[17]

The Argentine Air Force used them on Antarctica ^[18] since the 1970s with at least one of them deployed the whole year at Marambio Base ^[19]

Air Greenland uses one of its Twin Otters for winter supply flights to the Summit Camp polar research station

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 (22), Trans Maldivian Airways (15), Kenn Borek Air (42)^[20] and Scenic Airlines (11). Some 115 airlines operate smaller numbers of the aircraft including Yeti Airlines in Nepal, Malaysia Airlines which uses the Twin Otter exclusively for passenger and freight transportation to the Kelabit Highlands region in Sarawak, and in the United Kingdom the FlyBe franchise operator Loganair which uses the aircraft to service the island of Barra in the Hebrides islands. This scheduled service is unique as the aircraft lands on the beach and the schedule is partly influenced by the tide tables. The Twin Otter is also used for landing at the world's shortest commercial runway on the Caribbean island of Saba, Netherlands Antilles.

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

Transport Canada still owns three DHC-6 Twin Otters, but they now see very limited flying time, as their role in Coastal Surveillance has been replaced by a fleet of DHC-8 aircraft.^{[citation needed]}

The Twin Otter has been popular with commercial skydiving operations. It is able to carry up to 22 skydivers to over 13,500 ft^[21] (a large load compared to most other aircraft in the industry); presently, the Twin Otter is used in skydiving operations in many countries. The United States Air Force operates three Twin Otters for the United States Air Force Academy's skydiving team.

On September 25, 2008, the Series 400 Technology Demonstrator achieved "power on" status in advance of an official rollout.^[22]^[23] First flight of the Series 400 technical demonstrator, C-FDHT, took place October 1, 2008 at Victoria Airport.^[24]^[25] Two days later, the aircraft departed Victoria for a ferry flight to Orlando, Florida, site of the 2008 National Business Aviation Association (NBAA) Conference and exhibition. The first new build Series 400 Twin Otter (SN 845) made its first flight on February 16, 2010 in Calgary, Alberta.^[26] Transport Canada presented Viking Air Limited with an amended DHC-6 Type Certificate including the Series 400 on July 21, 2010.^[4]

v t e United States STOL and VTOL aircraft designations
Original sequence (1954-1962)	V-1 V-2 V-3
Tri-service sequence (1962-present)	V-1 V-2 V-3 V-4 V-5 V-6 V-7 V-8² XV-8 AV-8 AV-8B V-9 V-10 V-11 V-12² OV-12 FV-12 V-13¹ V-14¹ V-15 V-16³ V-17¹ V-18 V-19¹ V-20 V-21¹ V-22 V-23 V-24
¹ Not assigned • ² Assigned to multiple types • ³ Unofficial

Design and development

New production

Possible international Twin Otter production

Operational history

Variants

Operators/Former Operators

Civil operators

Military operators

Notable accidents and incidents

Specifications (300 series)

Specifications (400 series)

See also

References

External links