The de Havilland Canada DHC-6 Twin Otter is a Canadian STOL (Short Takeoff and Landing) utility aircraft developed by de Havilland Canada in the mid-1960s and still in production today. De Havilland Canada produced it from 1965 to 1988; Viking Air purchased the type certificate, then restarted production in 2008 before re-adopting the DHC name in 2022. In 2023 DHC restarted production of the 300 series, in addition to the Series 400 produced by Viking. The aircraft's fixed tricycle undercarriage, STOL capabilities, twin turboprop engines and high rate of climb have made it a successful commuter airliner, typically seating 18–20 passengers, as well as a cargo and medical evacuation aircraft. In addition, the Twin Otter has been popular with commercial skydiving operations, and is used by the United States Army Parachute Team and the 98th Flying Training Squadron of the United States Air Force.
Development of the aircraft began in 1964, with the first flight on 20 May 1965. A twin-engine replacement for the single-engine DHC-3 Otter retaining DHC's STOL qualities, its 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 550shp Pratt & Whitney Canada PT6A-20 turboprop in the early 1960s made the concept of a twin more feasible. A DHC-3 Otter with its piston engine replaced with two PT6A-4[1] engines had already flown in 1963. It had been extensively modified for STOL research.[2] To bush plane operators, the improved reliability of turboprop power and the improved performance of a twin-engine configuration made it an immediately popular alternative to the 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 numbers 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 for 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 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 engine that was flat rated to 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 subvariants (Series 310 for United Kingdom operators, Series 320 for Australian operators, etc.) sold before production in Toronto by de Havilland Canada ended in 1988.
In 1972, its unit cost was US$680,000,[3] In 1976, a new -300 would have cost $700,000 ($ million 31 years later) and is still worth more than $2.5 million in 2018 despite the -400 introduction, many years after the -300 production ceased.[4] 844 had been produced by the time the first production end run ended in 1988.[5] [6]
After Series 300 production ended, the remaining tooling was purchased by Viking Air of Victoria, British Columbia, 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 Aviation for all the out-of-production de Havilland Canada aircraft (DHC-1 through DHC-7).[7] The ownership of the certificates gives Viking the exclusive right to manufacture new aircraft.
On 17 July 2006, at the Farnborough Airshow, Viking Air announced its intention to offer a Series 400 Twin Otter. On 2 April 2007, Viking announced that with 27 orders and options in hand, it was restarting production of the Twin Otter, equipped with more powerful Pratt & Whitney Canada PT6A-34 engines.[8] As of November 2007, 40 firm orders and 10 options had been taken and a new final assembly plant was established in Calgary, Alberta.[9] [10] Zimex Aviation of Switzerland received the first new production aircraft, serial number 845, in July 2010.[11] [12] By mid-2014, Viking had built 55 new aircraft at its Calgary facility. The production rate as of summer 2014 was about 24 aircraft per year. In April 2015, Viking announced a reduction of the production rate to 18 aircraft per year.[13] On 17 June 2015, Viking further announced a partnership with a Chinese firm, Reignwood Aviation Group. The group will purchase 50 aircraft and become the exclusive representatives for new Series 400 Twin Otters in China.
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 systems, and use of composites for non load-bearing structures such as doors.[14]
The 100th Series 400 Twin Otter (MSN 944) was displayed at the July 2017 EAA AirVenture Oshkosh. Currently, 38% are operated as regional airliners, 31% in military aviation or special missions, 26% in industrial support and 5% in private air charter. Additionally, 70 are on regular landing gear wheels, 18 are configured as straight or amphibious floatplanes, 10 have tundra tires and 2 have wheel skis.[15]
In 2019, Viking started making plastic components for the Twin Otter by 3D printer to help reduce cost.[16] Twin Otter production was suspended in 2019 during the COVID-19 pandemic. In July 2022, DHC announced that it was reviewing the program and supply chain, with a decision on when to resume production expected "in the near future".[17] In 2023, its equipped price was $7.25M.[18]
In June 2023 Viking, now operating as De Haviland Canada started production of new DHC-6 Classic 300-G.[6]
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. Areas including Canada and the United States, (specifically Alaska) had much of the demand. Many Twin Otters still serve in the Arctic and subarctic, but they can also be found in Africa, Australia, Asia, Antarctica, and other regions where bush planes are the optimum means of travel. Their versatility and manoeuvrability have made them popular in areas with difficult flying environments such as Papua New Guinea. In Norway, the Twin Otter paved the way for the network of short-field airports, connecting rural areas with larger towns. The Twin Otter showed 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 (take-off, flight, and landing) per year.
A number of commuter airlines in the United States got their start by operating Twin Otters in scheduled passenger operations. Houston Metro Airlines (which later changed its name to Metro Airlines) constructed their own STOLport airstrip with a passenger terminal and maintenance hangar in Clear Lake City, Texas, near the Johnson Space Center. The Clear Lake City STOLport was specifically designed for Twin Otter operations. According to the February 1976 edition of the Official Airline Guide, Houston Metro operated 22 round-trip flights every weekday at this time between Clear Lake City (CLC) and Houston Intercontinental Airport, now George Bush Intercontinental Airport, in a scheduled passenger airline shuttle operation.[19] Houston Metro had agreements in place for connecting passenger feed services with Continental Airlines and Eastern Air Lines at Houston Intercontinental, with this major airport having a dedicated STOL landing area at the time specifically for Twin Otter flight operations. The Clear Lake City STOLport is no longer in existence.
The Walt Disney World resort in Florida was also served with scheduled airline flights operated with Twin Otter aircraft. The Walt Disney World Airport, also known as the Lake Buena Vista STOLport, was a private airfield constructed by The Walt Disney Company with Twin Otter operations in mind. In the early 1970s, Shawnee Airlines operated scheduled Twin Otter flights between the Disney resort and nearby Orlando Jetport, now Orlando International Airport, as well as to Tampa International Airport. This service by Shawnee Airlines is mentioned in the "Air Commuter Section" of the 6 September 1972 Eastern Air Lines system timetable as a connecting service to and from Eastern flights.[20] This STOL airfield is no longer in use.
Another commuter airline in the United States, Rocky Mountain Airways, operated Twin Otters from the Lake County Airport in Leadville, Colorado. At an elevation of above mean sea level, this airport is the highest airfield in the United States ever to have received scheduled passenger airline service, thus demonstrating the wide-ranging flight capabilities of the Twin Otter. Rocky Mountain Airways went on to become the worldwide launch customer for the larger, four-engine de Havilland Canada Dash 7 STOL turboprop, but continued to operate the Twin Otter, as well.
Larger scheduled passenger airlines based in the United States, Canada, Mexico, the Caribbean and Australia, particularly jetliner operators, also flew Twin Otters, with the aircraft providing connecting feeder service for these airlines. Jet aircraft operators which also flew the Twin Otter included Aeronaves de Mexico, Air BC, Alaska Airlines, ALM Antillean Airlines, Ansett Airlines, Cayman Airways, Frontier Airlines, LIAT, Norcanair, Nordair, Ozark Air Lines, Pacific Western Airlines, Quebecair, South Pacific Island Airways, Time Air, Transair, Trans Australia Airlines (TAA), Wardair and Wien Air Alaska.[21] [22] In many cases, the excellent operating economics of the Twin Otter allowed airlines large and small to provide scheduled passenger flights to communities that most likely would otherwise never have received air service.
Twin Otters are also a staple of Antarctic transportation.[23] 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 24–25 April 2001, two Twin Otters performed the first winter flight to Amundsen–Scott South Pole Station to perform a medical evacuation.[24] [25] [26] [27]
On 21–22 June 2016, Kenn Borek Air's Twin Otters performed the third winter evacuation flight to Amundsen–Scott South Pole Station to remove two people for medical reasons.[28]
The Argentine Air Force has used the Twin Otter in Antarctica[29] since the 1970s, with at least one of them deployed year-round at Marambio Base.[30] The Chilean Air Force has operated the type since 1980, usually having an example based at Presidente Frei Antarctic base of the South Shetland Islands.
Alfredo Stroessner, Paraguayan head of state from 1954 until 1989, used a Twin Otter as a presidential aircraft; although the Twin Otter remained in the Paraguayan Air Force inventory after he was deposed, subsequent presidents switched to other, private aircraft for official duties.[31]
As of August 2006, a total of 584 Twin Otter aircraft (all variants) remained in service worldwide. Major operators at the time included: Libyan Arab Airlines, Maldivian Air Taxi, Trans Maldivian Airways, Kenn Borek Air, and Grand Canyon Scenic Airlines. Some 115 airlines operated smaller numbers of the aircraft including Yeti Airlines in Nepal, Malaysia Airlines (which used the Twin Otter exclusively for passenger and freight transportation to the Kelabit Highlands region in Sarawak), and in the United Kingdom, the Scottish airline, Loganair which uses the aircraft to service the island of Barra in the Outer Hebrides. This daily scheduled service is unique as the aircraft lands on the beach and the schedule is partly influenced by the tide tables. Trials at Barra Airport with heavier planes than the Twin Otter, like the Short 360, failed because they sank in the sand. The Twin Otter is also used for landing at Juancho E. Yrausquin Airport, the world's shortest commercial runway, on the Caribbean island of Saba, Netherlands Antilles.
The Twin Otter has been popular with commercial skydiving operations. It can carry up to 22 skydivers to over (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 26 April 2001, the first ever air rescue during polar winter from the South Pole occurred with a ski-equipped Twin Otter operated by Kenn Borek Air.[32] [33] [34]
On 25 September 2008, the Series 400 Technology Demonstrator achieved "power on" status in advance of an official rollout.[35] [36] The first flight of the Series 400 technical demonstrator, C-FDHT, took place 1 October 2008, at Victoria International Airport.[37] [38]
Two days later, the aircraft departed Victoria, British Columbia 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 16 February 2010, in Calgary, Alberta.[39] Transport Canada presented Viking Air Limited with an amended DHC-6 Type Certificate including the Series 400 on 21 July 2010.[10] Six years after, in July 2016, 100 series 400 have been delivered to 34 customers operating in 29 countries.[40]
In June 2017, 125 have been made since restarting production in 2010.[41]
See main article: List of de Havilland Canada DHC-6 Twin Otter operators. In 2016, there were 281 Twin Otters in airline service with 26 new aircraft on order: 112 in North/South America, 106 in Asia Pacific and Middle East (16 orders), 38 in Europe (10 orders) and 25 in Africa.[49]
In 2018, a total of 270 Twin Otters were in airline service, and 14 on order: 111 in North/South America, 117 in the Asia Pacific and Middle East (14 orders), 26 in Europe and 13 in Africa.[50]
In 2020, there were a total of 315 Twin Otters worldwide with 220 in service, 95 in storage and 8 on order. By region there were 22 in Africa, 142 in Asia Pacific (8 orders), 37 in Europe, 4 in the Middle East and 110 in the Americas.[51]
The Twin Otter has been popular not only with bush operators as a replacement for the single-engine de Havilland Canada DHC-3 Otter but also with other civil and military customers, with over 890 aircraft built. Many commuter airlines in the United States got their start by flying the Twin Otter in scheduled passenger operations.
| Total | In service | Storage | Country | ||
| 56 | 21 | 35 | Maldives | ||
| 15 | 11 | 4 | Canada | ||
| 13 | 6 | 7 | United States | ||
| 11 | 10 | 1 | Maldives | ||
| 9 | 9 | 0 | Canada | ||
| 9 | 7 | 2 | Switzerland | ||
| AeroGeo | 8 | 0 | 8 | Russia | |
| Air Borealis (PAL Airlines) | 8 | 8 | 0 | Canada | |
| Air Adelphi | 7 | 6 | 1 | Saint Vincent and the Grenadines | |
| 7 | 7 | 0 | Canada | ||
| 7 | 5 | 2 | Argentina | ||
| AIRFAST Indonesia | 6 | 6 | 0 | Indonesia | |
| 6 | 5 | 1 | Indonesia | ||
| 6 | 5 | 1 | Maldives | ||
| 6 | 2 | 4 | Malaysia | ||
| 6 | 0 | 6 | Indonesia | ||
| Air Tuvalu | 1 | 0 | 1 | Tuvalu |
| Date | Flight | Location | Country | Event | ||||
|---|---|---|---|---|---|---|---|---|
| 23 November 1968 | 9 | United States | While landing, impacted light pole in fog, short of John Wayne Airport. | |||||
| 29 June 1972 | 5 | United States | Collided mid-air with a North Central Airlines Convair 580 carrying five, killing all.[53] | |||||
| 5 January 1975 | 13 | Argentina | Crashed due to bad weather and lack of a flight plan.[54] | |||||
| 9 January 1975 | 12 | United States | Collided with a Cessna 150, also killing its two occupants | |||||
| 3 May 1976 | Demonstration | 11 | Zambia | Crashed on take off | ||||
| 12 December 1976 | Allegheny Commuter Flight 977 | 3 | United States | Crashed short of the runway | ||||
| 18 January 1978 | 3 | United States | Crashed during a training flight[55] | |||||
| 2 September 1978 | Airwest Airlines | 11 | Canada | Approach loss of control after a corroded rod failed and a flap retracted | 2 | |||
| 18 November 1978 | Jonestown cult rescue | Guyana | Attacked by cultists while rescuing people; aircraft managed to successfully escape. Another aircraft did not leave and the occupants were shot dead[56] [57] | |||||
| 4 December 1978 | 2 | United States | Survivable impact on snow, severe icing and mountain-wave downdraft[58] | |||||
| 30 May 1979 | 17 | United States | 1 | |||||
| 24 July 1981 | Air Madagascar Flight 112 | 19 | Madagascar | Controlled flight into terrain (CFIT) into a mountain in cloudy conditions | ||||
| 31 July 1981 | 7 | Panama | Killed President Omar Torrijos,[59] cause disputed | |||||
| 21 February 1982 | 1 | United States | Emergency landing after a fire broke out on board[60] | 10 | ||||
| 11 March 1982 | 15 | Norway | ||||||
| 18 June 1986 | 20 | United States | Collided with a Helitech Bell 206, also killing its five occupants | |||||
| 4 August 1986 | 13 | St. Vincent and the Grenadines | Crashed into the Caribbean Sea. The aircraft was en route between St. Lucia and St. Vincent when it crashed due to poor weather conditions, while on approach. | |||||
| 28 October 1989 | Aloha Island Air Flight 1712 | 20 | United States | Crashed into a mountain on approach to Molokai Airport.[61] | ||||
| 12 April 1990 | 5 | Norway | Crashed in the ocean due to wind | |||||
| 22 April 1992 | 16 | United States | Fuel contamination, lost power and crashed near the runway end[62] | 6 | ||||
| 27 October 1993 | 6 | Norway | Controlled flight into terrain into forest on a hill during approach at night in bad weather | 13 | ||||
| 17 December 1994 | 28 | Papua New Guinea | Crashed en route,[63] striking a mountain at . | |||||
| 10 January 1995 | 14 | Indonesia | Disappeared in bad weather from Sultan Muhammad Salahudin Airport to Frans Sales Lega Airport, Ruteng. | |||||
| 30 November 1996 | 15 | Colombia | Crashed from Olaya Herrera Airport[64] | |||||
| 7 January 1997 | 3 | Samoa | 2 | |||||
| 24 March 2001 | 19 | French West Indies | Crashed near Gustaf III Airport, killing one on ground.[65] | |||||
| 26 May 2006 | Air São Tomé and Príncipe training flight | 4 | Airline's sole aircraft, registered S9-BAL, crashed during training flight.[66] | |||||
| 9 August 2007 | 20 | French Polynesia | Bound for Tahiti, crashed shortly after takeoff near Moorea Airport[67] | |||||
| 6 May 2007 | 9 | Egypt | ||||||
| 8 October 2008 | 18 | Nepal | Destroyed on landing at Tenzing-Hillary Airport[68] | 1 | ||||
| 2 August 2009 | 16 | Indonesia | Crashed about north of Oksibil.[69] | |||||
| 11 August 2009 | 13 | Kokoda Valley | Papua New Guinea | Crashed on a mountain whilst en route from Port Moresby to Kokoda.[70] | ||||
| 15 December 2010 | 22 | Bilandu Forest | Nepal | A Tara Air Twin Otter crashed after take-off on a domestic flight from Lamidanda to Kathmandu, Nepal[71] | ||||
| 20 January 2011 | 6 | El Capricho | Ecuador | |||||
| 22 September 2011 | 2 | Canada | Float plane crashed in the street, injuring seven.[72] | |||||
| 23 January 2013 | 3 | Antarctica | Skiplane lost en route from the South Pole to Terra Nova Bay.[73] [74] [75] | |||||
| 10 October 2013 | MASwings Flight 3002 | 2 | Malaysia | 14 | ||||
| 16 February 2014 | 18 | Nepal | En route to Jumla from Pokhara.[76] | |||||
| 20 September 2014 | Hevilift | 4 | Papua New Guinea | Crashed on landing[77] | 5 | |||
| 24 February 2016 | 23 | Nepal | Tara Air crashed after takeoff[78] | |||||
| 2 October 2015 | 10 | Indonesia | ||||||
| 30 August 2018 | 18 | Ethiopia | From Dire Dawa, crashed at a place called Nannawa[79] | |||||
| 4 | Indonesia | From Timika, crashed at Hoeya district[80] | ||||||
| 29 May 2022 | 22 | Nepal | Crashed after takeoff from Pokhara Airport | |||||
| 20 May 2023 | [not listed] | 2 | United States | Crashed into Half Moon Bay, California | ||||
| 27 December 2023 | Air Tindi Flight | 0 | Canada | Crashed 300 km NE of Yellowknife[81] |
| Series | 100[82] | 300 | 400[83] | |
|---|---|---|---|---|
| Cockpit crew | 1–2 | |||
| Seating | 20 | 19 | ||
| Length | 49 ft 6 in (15.09m) | |||
| Height | 19 ft 6 in / 5.94 m | |||
| Wing | span, area (AR) | |||
| Empty weight | 5,850l lb / 2,653 kg | 7,415 lb / 3,363 kg | 7,100 lb / 3,221 kg (no accommodation) | |
| MTOW | 10,500 lb / 4763 kg | 12,500 lb / 5,670 kg | ||
| Payload | 975 kg (2150 lb) over 1344 km (727 nm) | 1135 kg (2500 lb) over 1297 km (700 nm) 860 kg (1900 lb) over 1705 km (920 nm) | 1842 kg (4061 lb) over 185 km (100 nm) 1375 kg (3031 lb) over 741 km (400 nm) | |
| Fuel capacity | 378 US gal / 1466 L, 2,590 lb / 1,175 kg | |||
| Turboprops (×2) | P&WC PT6A-20 | PT6A-27 | PT6A-34 | |
| Unit Power | 431 kW / 578shp | 460 kW / 620shp | ||
| Max. Cruise | 297 km/h / 160kn | 338 km/h / 182kn | (FL100) | |
| Takeoff to 50 ft | STOL 1,200 ft / 366 m; CTOL 1,490 ft / 454 m; [84] | |||
| Landing from 50 ft | STOL 1,050 ft / 320 m; CTOL 1,510 ft / 460 m; | |||
| Stall Speed | 65 mph | |||
| Ferry Range | 771 nmi / 1,427 km | 799 nmi / 1480 km | ||
| Endurance | 6.94 h | |||
| Ceiling | 25,000 ft / 7,620 m | |||
| Climb rate | ||||
| FL100 fuel burn | /hour | |||
| Power/mass | ||||
