The Twin Otter has many claims to fame, but one fact stands out: it has been in production (with a notable break) longer than any other commercial aircraft in the history of aviation. Malcolm Ginsberg details its first incarnation
The Twin Otter is rapidly approaching the milestone of 1,000 built. The first part of its story is production from 1965 through to 1988 at Downsville in Toronto, Ontario – the headquarters of de Havilland Canada – with 844 legacy DHC-6s built (of which around 470 are still in service today). The second part, which will be covered in the next issue of Aviation News, is the production of more than 150 Viking Twin Otter Series 400s built and assembled in Calgary, Alberta, and Victoria, British Columbia since 2010.
The Twin Otter largely owes its existence to the Vietnam War. The original single-engined DHC-3 Otter utility aircraft first flew in December 1951, with a total of 466 built before production ceased in 1967; 184 of these went to the US Army under the designation U-1A. The single Otter proved to be a fine military support aircraft, but under actual combat conditions in Vietnam, pilots complained of its vulnerability with a single engine and, while fine for bulky cargo, it had limited lift capability. A tricycle undercarriage was also ideally required to deal with crosswind landings.
In July 1963, a de Havilland Canada working group was established to look into having a twin-engined version of the Otter, featuring the Pratt & Whitney PT6 turboprop engine that was being developed at the time. It is amazing to think that today, advanced versions of the engine are still being produced, having powered around 100 aircraft types and also the Lotus 56 Indianapolis Special and 1971 56B Formula One racing cars. More than 50,000 PT6s have been manufactured to date.
The newly designed twin-engine aircraft had its predecessor windows and also the hgh wing configuration. One difference was the tailfin, the rather smooth application of the original aircraft giving way to an angular appendage. The box-like fuselage cross-section of the DHC-3 was retained for the DHC-6 but lengthened from 16ft 5in to 18ft 6in. The internal height at just 5ft 2in was the same, which in airline use meant always reminding passengers to watch their head! Sales were initially aimed at the military and government organisations, but in time it proved to be a fine commuter aircraft with capacity for 20 passenger seats though regulations in most countries require carriage of a cabin attendant. Many operators fly with 19 passenger seats and no cabin attendant.
Development of the aircraft began in 1964, with the first flight on May 20, 1965. As a twin-engine replacement for the single-engine DHC-3 Otter it incorporated DHC’s huge experience of STOL (short take-off and landing) qualities, its design features including double-slotted trailing edge flaps and ailerons that work in unison with the flaps to boost runway performance. The availability of the 550shp Pratt & Whitney Canada PT6A-20 turboprop was the final piece in the jigsaw. In 1963, during the development phase, a DHC-3 Otter was modified with a pair of the new Pratt & Whitney turbines, serving a very useful purpose for STOL research.
SERIES PRODUCTION
The first four aircraft produced were designated Series 1, indicating that they were prototype aircraft. The initial production run consisted of 110 Series 100 aircraft, serial numbers 5 to 115 inclusive. In 1968, Series 200 production began with serial number 116. Changes made at the beginning of the Series 200 programme 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 550shp 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 680shp engine that was flat-rated to 620shp for use in the Series 300 Twin Otter. The Series 300 proved to be the most successful variant by far, with 614 aircraft and their sub variants (minor modifications for the UK market were incorporated under the Series 310, and for Australian operators, Series 320) sold before production ended in 1988. Twin Otters could be delivered directly from the factory with floats, skis or tricycle landing gear fittings, making them adaptable bush planes for remote northern areas of Canada and the United States (specifically Alaska). These regions generated much of the demand. Many Twin Otters still serve in the far north, but they can also be found on all seven continents where robust and reliable aircraft are the optimum means of travel. Their versatility and manoeuvrability have made them popular in areas with difficult environments, such as Africa and the Middle East, and more recently Papua New Guinea and Nepal. Floatplane versions are seen all around the world at resorts, a capability highlighted by a show-stopping demonstration flight into London’s Royal Docks during the 2006 World Travel Market to promote the use of the aircraft in the Greek islands. In the Maldives archipelago after landing at Male International Airport, it is just a short walk to the seaplane base from which the Twin Otter air taxi delivers visitors directly to their five-star luxury holiday resort.
In Norway, the Twin Otter paved the way for the network of short-field airports, connecting rural areas with larger towns. The aircraft 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 the type, with 18. During one period of its tenure in Norway, the Twin Otter fleet achieved more than 96,000 cycles (takeoff, flight and landing) per year.
Several commuter airlines in the United States made their start by operating Twin Otters on scheduled passenger operations. Houston Metro Airlines (later just Metro Airlines) constructed its own ‘STOLport’ airstrip with a passenger terminal and maintenance hangar, near the NASA Johnson Space Center, in Clear Lake City, Texas. According to the February 1976 edition of the Official Airline Guide, Houston Metro operated 22 round-trip flights every weekday between Clear Lake City and Houston Intercontinental Airport (now Houston George Bush Intercontinental Airport) in a scheduled passenger airline shuttle operation. Houston Metro had agreements in place as a feeder airline for connecting passenger services with Continental Airlines and Eastern Airlines 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 closed in the late 1980s and is no longer in existence, having been developed for housing.
MICKEY MOUSE OPERATION
The Walt Disney World resort in Florida was also serviced by 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 offered scheduled Twin Otter flights between the Disney resort and nearby Orlando Jetport (now Orlando International Airport), as well as to Tampa International Airport. The service was operated for a time as a connecting service to and from Eastern Airlines flights. This Lake Buena Vista airfield closed after only two years of operation due to construction of the resort’s monorail.
Another commuter airline in the US, Rocky Mountain Airways, operated Twin Otters from the Lake County Airport in Leadville, Colorado. At an elevation of 9,927ft above mean sea level, this airport is the highest airfield in the US 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 DHC-7 Dash 7 STOL turboprop, but continued to operate the Twin Otter as well.
Larger scheduled passenger airlines (mostly jet operators) based in the United States, Canada, Mexico, the Caribbean and Australia, also flew Twin Otters, with the aircraft providing connecting feeder services. These included Aeronaves de México, 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 (Canada), Trans Australia Airlines (TAA), Wardair Canada and Wien Air Alaska. In many cases, the excellent operating economics of the Twin Otter allowed airlines large and small to provide scheduled passenger flights to remote communities that most likely would otherwise never have received air service.
UK aircraft were initially certificated as single-crew and the author vividly recalls sitting in the right-hand seat downwind at Gatwick as the pilot waited for a slot between the jumbos. It was a quick landing and, with permission, a turn-off was granted at the normal runway second access point. When two pilots became mandatory the ‘safety’ cabin staff member became redundant, the second pilot taking on those duties.
IN UNIFORM
As military transports, Twin Otters have been used by air forces, army flying services and many NGO agencies all over the world. According to the published records, Twin Otters have operated for about 20 military wings and government bodies. In 1971, the Canadian Forces took nine Twin Otters for search and rescue use. The Chilean Air Force was one of the earliest and largest customers for the DHC-6 and the aircraft found much favour in Latin America with other users being the Colombian Police Force, Ecuadorian Air Force, Panama National Air and Naval Service, Paraguayan Air Force, and the Peru Air Force.
It was expected as the aircraft was being developed that a large order from the US military would be forthcoming, because the original Otter had been a success under difficult circumstances. However, politics intervened, as allegedly did American protectionism. A possible US order for 100 Twin Otters was lost when the performance specification was changed during the tender process, allowing the Beech King Air 200 into the C-XX competition with an attractive price. The Beech aircraft won in 1974 and only a handful of de Havilland Canada-built DHC-6s have served with US forces, including five UV-18As with the army, two of which were transferred to the US Navy. Three UV-18Bs are used for parachute training at the USAF Academy as well as by the service’s ‘Wings of Blue’ parachute team. Twin Otters have also been utilised by the USAF’s special operations command.
NASA’s Glenn Research Center in Ohio uses one aircraft, principally for icing research. Another interesting operator is the National Oceanic and Atmospheric Administration (NOAA) which uses four Series 300 aircraft for airborne marine mammal, hydrological, remote sensing, air chemistry and emergency response programmes.
Twin Otters are also a staple of Arctic and Antarctic transportation. Four Twin Otters are employed by the British Antarctic Survey on research and supply flights, and several are flown by the United States Antarctic Programme via contract with Kenn Borek Air. Over April 24-25, 2001, two Twin Otters performed the first winter flight to Amundsen-Scott South Pole Station to perform a medical evacuation.
The Argentine Air Force has used the Twin Otter in Antarctica since the 1970s, with at least one of them deployed year-round at Marambio Base. The Chilean Air Force has operated the type since 1967, usually having an example based at Presidente Eduardo Frei Montalva Antarctic base on the South Shetland Islands. Air Greenland uses one of its Twin Otters for winter supply flights to the Summit Camp polar research station.
STILL GOING STRONG
Today, around 520 Twin Otter aircraft (all variants) remain in service worldwide. Major operators include Trans Maldivian Airways, which merged with Maldivian Air Taxi in 2013 and now has over 48 (including three Series 400s). Kenn Borek Air has 21 and Scenic Airlines in Arizona, 11. Some 115 airlines operate smaller numbers of the aircraft including Yeti Airlines in Nepal and Malaysia Airlines, which uses the Twin Otter exclusively for passenger and freight transportation to the Kelabit Highlands region in Sarawak. In the UK, the Scottish airline Loganair utilises the aircraft to service the island of Barra in the Hebrides. This daily service is unique as the aircraft lands on the beach and the schedule is partly influenced by the tide tables. Trials in Barra with heavier aircraft such as the Short 360 failed because they sank in the sand. Loganair also operates the world’s shortest air route, Westray to Papa Westray in the Orkney Islands to the northeast of the Scottish mainland – a distance of 1.7 miles. Flights on the route are scheduled for one-and-a-half-minutes, and actual flying time is closer to one minute. The record for the fastest flight is 47 seconds. Loganair has operated a classic Twin Otter since 1994 and in 2015 took delivery on behalf of the Scottish government of two Series 400 aircraft that are used for scheduled services and air ambulance work.
The Twin Otter is also used for landing at the world’s shortest commercial runway on the Caribbean island of Saba, Netherlands Antilles, which is 1,312ft long, flanked on one side by high hills, with cliffs that drop into the sea at both ends.
The Twin Otter has been popular with commercial skydiving operations, as it can carry up to 22 skydivers (a large load compared with most other aircraft in the industry) to more than 17,000ft In the 1970s, the UK Civil Aviation Authority certificated the Twin Otter for Brymon Airways to use from its then grass strip at Plymouth to Jersey, Guernsey and various French Channel airports and for the Scilly Islands. Newquay-Cornwall was also in the schedule and it was possible to link up with the airline’s Heathrow service (initially a Herald but later a Dash 7) to enable a day return.
Brymon operated up to ten Twin Otters at one time and, unlike the B-N Islander, which it also flew, passengers were not weighed before boarding. A Brymon aircraft made a landing at Heathrow in this period, given special permission due to an emergency at RAF St Mawgan, now Cornwall-Newquay Airport. It is probably the smallest airline aircraft ever to go into the airport.
With the demise of Brymon, Isles of Scilly Skybus took over the operation and currently (pre COVID-19) operates four as 19-seaters from St Mary’s/Isles of Scilly to Exeter, Land’s End (Penzance) and Cornwall-Newquay airports.
Why has the de Havilland Canada DHC-6 been so successful over the last 55 years? Its greatest virtue is its simplicity, including the lack of pressurisation, plus the availability of Pratt & Whitney PT6 engines and maintenance know-how worldwide. It is rough and tough and is (fairly) comfortable. Although its production stopped for more than two decades, it has had a resurrection and continued success.
Part Two will tell the story of the Twin Otter Series 400.
