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Viking Twin Otter

Posted on September 23 2021

Viking Twin Otter user+1@localho… Thu, 09/23/2021 - 21:17

The DHC-6 Twin Otter is a high-wing, twin-engine turboprop airplane that is currently produced by Canadian manufacturer Viking Air Ltd. Described as being “the longest-serving 19-passenger aircraft in the world” and a “short takeoff and landing (STOL) commuter,” the first version of the Twin Otter—which included the prototype and four pre-production airplanes—was designated the DHC-6 Series 1 and certified in April 1966, while the DHC-6 Series 100 was the first production series of the airframe and was certified in July 1966. Prior to receiving certification, the Twin Otter’s first flight took place on May 20, 1965. Subsequent to the Series 1 and 100, owners de Havilland and Viking developed and certified a number of additional variants of the DHC-6, including the Series 200, 300 and, most recently, the 400. From 1966 to 1986, the DHC-6 type certificate was held be de Havilland Aircraft of Canada Ltd., with the type certificate updated in 1986 to reflect the fact that the company had become a subsidiary of Boeing Canada Ltd. Subsequently, the type certificate was transferred in 1988 to Boeing of Canada Ltd. (de Havilland division), in 1992 to de Havilland Inc. and in 1998 to Bombardier Inc.

The type certificates for all out-of-production De Havilland airframes—DHC-1 to DHC-7—were purchased by Viking in 2005, with the transfer of those certificates occurring in 2006 and the company announcing plans to produce the Viking Series 400 Twin Otter in 2007. First flight of a Series 400 demonstrator—a modified DHC-6 Series 300 —took place on Oct. 1, 2008, while the first flight of a Viking-produced Series 400 airframe occurred a little more than a year later on Feb. 16, 2010, in Calgary, Alberta. That latter flight was performed by airframe MSN 845, which was registered as C-FMJO, an airframe that was subsequently delivered to Zimex Aviation of Switzerland in January 2011, registered as HB-LUX and, according to Viking, has performed corporate charter and “essential humanitarian relief services in Africa and the Middle East” since it was delivered. While MSN 845 performed the first flight and was ultimately delivered to Zimex, the first delivery of a Series 400 Twin Otter was MSN 846, which was delivered to Air Seychelles on Dec. 24, 2010.

Certification Dates (Transport Canada)

DHC-6 Series 1

April 7, 1966

DHC-6 Series 100/110

July 29, 1966

DHC-6 Series 200/210

March 29, 1968

DHC-6 Series 300/310

April 26, 1969

DHC-6 Series 320

Jan. 23, 1970*

DHC-6 Series 400

June 24, 2010

                                                *Australian Department of Civil Aviation Certification

Cabin Capacity, Dimensions and Outfitting

According to the Transport Canada type certificate data sheet (TCDS) for the type, the passenger capacity of the DHC-6 variants ranges from 15 and 21, with the prototype and pre-production Series 1 limited the lower end of that passenger capacity range. The DHC-6 Series 100/110 and 200/210 increase the capacity to 20, while the Series 300/310/320 incrementally increases it further to 21. The DHC-6 Series 400 has a certified occupant capacity of 19—excluding the pilot seats—with those passengers accommodated in a cabin that has a usable volume of 384 ft.3 and a height, length and width of 4 ft. 11 in., 18 ft. 5 in. and 5 ft. 9 in., respectively. Passengers enter the cabin through an entry door that has a height of 50 in. and width of 56 in., with additional pilot doors located in the forward portion of the fuselage. The standard configuration of the Series 400’s cabin is the 19-seat commuter interior, which is supplemented by “standard options” for corporate shuttle, executive and VIP configurations. Promoted for its ability to be quickly reconfigured—and the associated benefits in turnaround time—additional configurations include an eight-seat executive layout, as well as a “specialized interior for parachuting.” According to Viking, the reconfiguration of the cabin can be accomplished without the need for special equipment or tools. In addition to the space in the cabin for passenger seating, the airframe has two baggage areas, one located forward of the flight deck and the other aft of the passenger cabin. On the Series 400, the forward storage area has a usable baggage volume of 35 ft.3, while the aft baggage has a greater volume of 88 ft.3

A number of outfitting options are available for the Series 400 Twin Otter cabin, options which are applicable to operators carrying both cargo and passengers, and which involve emergency egress, passenger comfort and supplemental oxygen. For passenger-carrying operators, a cabin emergency lighting system—which provides enhanced lighting—is available should an emergency evacuation become necessary. Operators also have the option of installing a wireless headset system into the cabin, with that system being provisioned for eight headsets. Also available is supplemental oxygen for both crew and passengers, both of which are designed to support operations above 10,000 ft. The optional crew oxygen system has a “standard duration of 160 min.,” and consists of a single oxygen cylinder that is installed in the airplane’s forward nose compartment and a pair of constant-flow oxygen masks. The crew oxygen system can be further enhanced through the installation of a larger oxygen tank and a quick-donning mask system. For passenger use, the optional oxygen system includes two oxygen cylinders in the rear baggage compartment and 20 constant-flow masks that are located throughout the cabin in overhead pouches, with the standard duration of oxygen provided being 90 min.

In addition to the configuration options noted above, a number of cabin options are also available that increase the utility of the cabin, as well as others that increase the comfort of the pilot(s). With reference to the latter options, snap and vista-type window vents are available to increase air circulation within the cockpit, with those vents mounted in the cockpit door window. Supplementing the pilot comfort benefits of those vents are optional electric fans that can be installed above the pilot and co-pilot seats. Viking also promotes a number of options for the interiors of executive and VIP-configured Series 400 Twin Otters, options such as an aft lavatory and an external lavatory service panel, fold-out table assemblies and a galley. Marketed as complimenting the “VIP club seating” that is located in the forward portion of the cabin, the fold-out table assembly option installs a pair of sidewall-mounted pull-out table assemblies. The optional galley—which has “provisions” for a microwave and cabinets for storage—would be located in the aft portion of the cabin on the right side, while the aft lavatory occupies part of the space that would otherwise be part of the aft baggage compartment. Described as being a chemical lavatory that can be removed in order to be serviced, the Series 400’s optional lavatory features a door and folding wall “in the rear cabin bulkhead,” while requiring the removal of a middle commuter seat. Additionally, access to the previously mentioned baggage compartment from the cabin can be accommodated through the installation of a rear cabin door at the center of the rear bulkhead, with its installation requiring the removal of “a middle bulkhead passenger seat.”

For operators carrying both passengers and cargo—as well as all-cargo operators—cabin options include a passenger-cargo combi configuration and a third-rail seat track which enables the right side of the cabin “to be configured with a single seat”—supplementing the standard double-seat arrangement—with the seat track also being necessary for the airframe’s cargo loading system. Beyond requiring the third-rail seat track, the cargo loading system’s components include a ball mat system and rollers that extend the “length of the cabin,” with the system located “on top of and secured to the existing seat rails.” From a capabilities standpoint, the system is described as giving operators the ability to roll small pallets “forward and aft during aerial resupply operations,” while the floor rollers themselves have a 5,000-lb. breaking strength. Also available are roll transfer balls at the entrance and a static line “with each 20-in. section rated at 500 lb.” The existing floor panels found in the cockpit and cabin can also be “covered and protected” by an abrasion-resistant coin mat floor covering, and cargo operations enhanced by 18 X 5.5-ft. webbed nylon cargo net that has both loop and clip fittings. A number of multidoor configuration options also exist, “including standard airstair, folding and roll-up,” with larger access doors such as barn and roller doors also available as options for the Series 400 airframe.

Avionics

All series of the DHC-6 are certified for single-pilot operations, with the Series 400 equipped with Honeywell’s Primus Apex Integrated Flight Deck as standard. The hardware that comprises the Primus Apex includes four active matrix liquid crystal displays (AMLCD)—two primary flight displays (PFD) and two multifunction displays (MFD)—an air data attitude heading reference system (ADAHRS), Class A terrain awareness and warning system (TAWS), distance measuring equipment (DME), dual GPS units and Mode S transponders, multi-mode digital radios, traffic alert and collision avoidance system (TCAS) and radar altimeter and weather radar systems. Beyond that hardware, the Series 400 Twin Otter has additional flight deck systems such as cockpit voice and flight data recorders, an emergency locator transmitter (ELT), magnetic standby compass and standby instrument system.

Supplementing the standard avionics of the Series 400 Twin Otter are a number of optional features that can increase the safety and the utility of the airframe. Those options include the ability to display electronic charts and maps, non-emergency checklists and XM aviation weather on the MFD. The TCAS I system that is standard can be upgraded to a TCAS II system that has traffic advisory (TA) and resolution advisory (RA) features, with a three-axis autopilot that incorporates an integral yaw damper also available as an option. That latter system requires the installation of a bracket, bridle cables, controller, servo, software load and switching. The navigation of the Twin Otter can be further enhanced through the installation of a synthetic vision system, as well as software upgrades to the Aircraft Personality Module (APM) that enable localizer performance with vertical guidance (LPV) approaches and coupled vertical navigation (VNAV). Synthetic vision capabilities are provided by another piece of Honeywell hardware—the “Smart View” synthetic vision system—which provides the pilot(s) a three-dimensional view of the surrounding topography on the Apex’s PFD or MFD. The APM upgrade that enables the coupled VNAV capabilities enhances the vertical modes of the flight director through “the introduction of modes that couple the FMS [flight management system] vertical flight plan to the flight director,” while another APM upgrade allows for the use of the FAA’s wide area augmentation system (WAAS) to perform LPV approaches.

Communication options for the Series 400 include Latitude Technologies’ SkyNode System which enables satellite communications and “real-time aircraft monitoring.” Honeywell’s KHD 1050 high-frequency (HF) radio and a very-high-frequency (VHF)-FM transceiver (marine radio) are also available, the latter of which allows airplanes to contact land stations and marine vessels. An optional feature for float-equipped Series 400 airframes is a float-mounted depth sounder which displays water depth on a cockpit display, with avionics redundancy able to be provided by a second radar altimeter and automatic direction finder (ADF). Another option that is featured alongside the airplane monitoring and satellite communications capabilities is the “capture” of engine and flight parameters that are then available for wireless download.

Mission and Performance

Viking promotes the reliability and versatility of the Series 400 Twin Otter, including the ability of the airframe to be used by numerous types of commercial, private and special-mission operators performing missions such as cargo and passenger carriage, as well as skydiving. In addition to the types of missions that the Series 400 variant is capable of performing, the manufacturer also promotes the types of conditions and places that is able to operate in, places such as jungles and Antarctica.

Because the Twin Otter can be equipped with wheels, skis and floats, the maximum operating speeds of the Series 1, 100/110, 200/210 and 300/310/320 differ depending upon the type of landing gear that a particular airframe is equipped with. When equipped as a landplane, the Series 1, 100 and 200 are limited to a never-exceed speed (VNE) of 202 kt. calibrated airspeed (KCAS), a limitation that is decreased to 183 KCAS when an airframe is operated as either a floatplane or skiplane. The maximum operating limit airspeed (VMO) of the Series 300 variant does not differ based on the type landing gear fitted, but by whether a particular airframe has modification 6/1291 incorporated. When that modification has not been performed, the sea-level VMO for all Series 300 airframes—regardless of the type of landing gear—is 160 KCAS, an airspeed that decreases to 115 KCAS at 25,000 ft. According to the Transport Canada TCDS, that VMO is increased to 170 KCAS from sea level to 6,700 ft.—an increase that is depicted on the TCDS as applying only to landplanes—while the airspeed limit at 25,000 ft. is the same as non-modified airplanes. Airspeed limits for the DHC-6 Series 400 are also only provided for land-based versions, with VMO from sea level to 6,700 ft. and 25,000 ft. being the same as those of the post-modification Series 300 airframes. Although the maximum operating speeds differ based on the factors listed above, all DHC-6 variants are limited to a common 25,000-ft. maximum operating altitude “when supplementary breathing equipment is provided for all occupants in accordance with operating rules.”

Beyond its certified performance limits, Viking also publishes a number of other performance figures for the Series 400, including an en route climb rate at sea level—assuming that both engines are operating at the maximum climb power—of 1,600 ft./min. When carrying zero payload and operating with the standard fuel tanks, the Series 400 has a maximum range of 775 nm, a figure that is increased to 980 nm when long-range tanks are installed. Similarly, that variant’s maximum endurance—also based on standard and long-range fuel tanks—are promoted as 7 hr. 10 min. and 9 hr., respectively. At the variant’s maximum cruise speed, the Series 400 can carry 4,061 lb. of payload 100 nm and 3,031 lb. of payload 400 nm. Assuming that both engines are operating and the airframe is equipped with wheeled landing gear, the takeoff distance to 50 ft. is 1,490 ft., a distance that is promoted by Viking as being 45%, 20% and 13% better than the Cessna Grand Caravan, Let L-410 and Dornier 228NG, respectively. When configured as a seaplane with floats, the takeoff and landing performance is noted as being valuable, enabling operations from “small lakes and rivers.”

Variants

DHC-6 Twin Otter Specifications

Type Designation

DHC-6 Series 1

DHC-6 Series 100/110

DHC-6 Series 200/210

DHC-6 Series 300/310/320

DHC-6 Series 400

Maximum Passenger Capacity

15

20

21

19

Maximum Range

 

980

Engine (1x)

Pratt & Whitney Canada

PT6A-20

PT6A-27

PT6A-34

Takeoff and Maximum Continuous Power (shp)

550

620

Maximum Takeoff Weight (MTOW)(lb.)

11,000

11,5793/11,6004

12,500

Maximum Landing Weight (lb.)

10,0001/11,0002

11,4003/11,6004

12,3003/12,5004

12,300

Usable Fuel Capacity (gal.)

358

378

Wingspan

65 ft.

Wing Area (ft.2)

 

420 ft.2

Length (ft.)

51 ft. 9 in.

Height (ft.)

19 ft. 6 in.

1 Skiplane

2 Landplane and floatplane

3 Landplane and skiplane

4 Floatplane

PT6A Engines and Hartzell Propellers

Despite the changes that have been made to the Twin Otter, each variant of the DHC-6 type has been certified to be powered by a variant of Pratt & Whitney Canada’s PT6A engine. The Series 1, 100/110 and 200/210 are powered by the PT6A-20, an engine that has a maximum continuous and takeoff rating of 550 shp. Comparatively, the PT6A engines approved for the Series 300/310/320 and 400—the PT6A-27 and -34, respectively—have a common maximum continuous and takeoff rating of 620 shp. In spite of the differences in the amount of shaft horsepower that those engines can produce, all three PT6A variants certified for the DHC-6 are free turbine turboprops that have common components which include a single annular combustion chamber, single-stage gas generator and power turbines and a three axial plus one centrifugal stage compressor.

Those engines power a pair of Hartzell propellers, with the three-blade, constant-speed HC-B3TN-3DY propellers found on the Series 400 capable of reversible pitch and being fully feathered, while having a nominal diameter of 8 ft. 6 in.

DHC-6 Series 1/100/110/200/210/300/310/320

In addition to having the lowest passenger capacity, the DHC-6 Series 1 also has the lowest maximum weights and usable fuel capacity of any DHC-6 variant, specifications that are increased on subsequent variants of the type. While all variants following the Series 1 have a common usable fuel capacity of 378 gal., the maximum weights—takeoff and landing—differ between the Series 100, 200, 300 and 400, with those weights being further differentiated based on whether an airplane is equipped with floats, skis or wheeled landing gear. While the Series 100/110 and 200/210 are limited to maximum takeoff and landing weights of 11,579 lb. and 11,400 lb. as a landplane and skiplane, a floatplane increases those limitations to a common 11,600 lb. For the Series 100/110, those increased weights in comparison to the Series 1 are predicated on the incorporation of modification 6/1020 which involves “fuselage beam [and] front wing spar reinforcing.” When that modification is not incorporated, the 11,000-lb. maximum takeoff and landing weights of the Series 1 are retained.

The MTOW and maximum landing weights are further increased on the Series 300, with the latter again differentiated based on the type of landing gear that an airframe is fitted with. When equipped as a landplane or skiplane, the maximum landing weight is limited to 12,300 lb., a limitation is increased a further 200 lb. on Series 300 airplanes equipped with floats.

DHC-6 Series 400

Described by Viking as “pick[ing] up where the original De Havilland Series 300 Twin Otter left off,” more than 800 modifications and upgrades were made to the DHC-6 Series 400 in comparison to “the original production model,” upgrades that include the previously mentioned PT6A engines and Honeywell Primus Apex avionics, as well as the use of light-emitting diode (LED) external and internal lighting. While the Series 400 retains the same 378-gal. usable fuel capacity as the Series 300, Viking promotes the airframe as having the option of being equipped with aluminum wing tip tanks which are “integral to the wing[,] make no change to the wing contour” and carry an additional 89 gal. of fuel. Another Series 300 specification that is retained by the current-generation Twin Otter is the 12,500-lb. maximum takeoff weight (MTOW).

Beyond the avionics, cabin, and fuel tank options available for the Series 400, options also exist for the airframe, flight controls and type of landing gear, as well as others that enhance the airframe’s capabilities in colder climates. The options for cold-weather operations include a deice package that has three options—electrically heated propellers and windshields, as well as tail and wing deice—and enables the airplane to be certified for flight into known icing (FIKI) conditions. Another cold-weather option is promoted as “providing warming in sub-zero environments” to components that are required for starting the engines such as the battery and MFD. An “enhanced protective coating” option provides added protection for long-term operations conducted in “highly corrosive environments,” while stainless steel flight control cables—in comparison to the standard carbon steel cables—are also suggested by the manufacturer for operators in “saline environments.”

Of the landing gear options for the Series 400—floats, wheel skis and wheeled landing gear—the wheeled skis option is described by Viking as allowing for operations on ice and snow and hard surfaces, with the system itself being hydraulically operated and requiring that the propellers have pitch latches installed. Also available is intermediate floatation gear, which is described as enabling soft-field landings by installing larger main and nose gear tires, while retaining the “standard 11 X 12 in. wheel rims.” Although the wheel rims are retained along with the installation of the larger tires, the size of the nose fork is increased to accommodate the larger nose-gear tire.

According to Viking, for Twin Otter operators seeking to utilize their airplane(s) as floatplanes, two different types of floats—amphibious and straight floats—and installation options are available, with the former type of floats “allow[ing] [for] flight between runways and seaports or lakes.” Both amphibious (Wipline 13000) and straight floats (Wipeline 13000SEA) can be installed as part of straight and amphibious floatplane conversions, with those conversions requiring the installation of three options: stainless-steel flight control cables, float reinforcements and propeller pitch latches that are “non de-ice.” Supplementing those changes on airframes receiving the amphibious floatplane conversion is the installation of an amphibious hydraulic system. In lieu of those conversions, amphibious and straight floats can be provided “for operators who want a different landing gear configuration.” However, Viking notes that the changes noted above must be installed for operators to utilize either type of floats.

Viking 400S Seaplane

Beyond the conversion options and the ability to install floats as needed per the above requirements, Viking also promotes a float-equipped Series 400 airframe that is optimized for commercial seaplane operations. Marketed as the Viking 400S Seaplane, it is described as being “specifically designed as an economical seaplane for commercial operations on short-to-medium flight segments.” From an economic perspective, the manufacturer states that an airframe configured in the standard 19-passenger layout can break even with “under nine passengers under typical operating conditions.” Further described as being “optimized for quick turnaround between cycles,” certain features of the 400S enable those quick turnaround times, while others reduce airplane weight and consequently increase performance. Features of the 400S that allow for quick turnarounds include a battery which is dedicated to the avionics system and provides power to it while the airplane is not airborne, while double swing-out doors located at the aft passenger entrance—which provide access to the cabin and baggage compartment—allow for “quick loading.”

From a performance perspective, in comparison to Series 400 airframes configured for “complex utility or special-mission operations,” the 400S is able to carry 17 passengers 150 nm with “typical reserves” because of the weight reduction provided by the airframe’s floats. A number of other performance figures have been released for the Viking 400S, with those figures based on the assumption of international standard atmosphere (ISA) +10 conditions, an empty weight of 8,150 lb. and a standard airplane configured with 17 commuter seats. For takeoff and landing, those criteria are supplemented by assumptions of a calm water surface, both engines operating at takeoff power “throughout,” sea-level altitude and zero wind, with the takeoff and landing distances to and from 50 ft. noted as 2,247 ft. and 1,741 ft., respectively. The respective ISA +10 maximum cruise speeds at 2,000 ft., 4,000 ft. and 8,000 ft. are 153 kt. true airspeed (KTAS), 154 KTAS and 156.5 KTAS. As was noted above with respect to payload-versus-range considerations, the distance that the airplane can fly is inversely proportional to the amount of payload carried, with the 400S capable of a 50-nm range when carrying 3,751 lb. of payload and a 200-nm range when the payload figure is reduced to 3,143 lb. In between those ranges, 100 nm and 150 nm ranges are possible with payloads of 3,533 lb. and 3,349 lb. Those payload-versus-range figures are based on a fuel allowance for taxi, takeoff and landing of 25 lb.; an instrument flight rules (IFR) fuel reserve of 220 lb., fuel usage per the “engine manufacturer’s specification,” climbing at maximum power and descending at 500 ft. per minute and cruising at the maximum cruise power (at 5,000 ft. for the 50 nm and 100-nm segments, and at 8,000 ft. for the 150 nm and 200 nm segments).

Special-Mission Equipped Series 400 Twin Otter

In addition to commercial applications for the Series 400 Twin Otter, the variant is also promoted as being able to perform a number of special-mission operations, including aerial photography, air ambulance, cloud seeding, environmental data collection, extraction and insertion, flight calibration and inspection, geographical survey; intelligence, surveillance and reconnaissance (ISR); maritime surveillance patrol, oil pipeline surveillance and oil spill detection, search and rescue (SAR) and special operations parachuting. Marketed as the Guardian 400, qualities of the airframe such as its acquisition and operating costs, endurance and low-airspeed maneuvering characteristics and the ability to perform short-field takeoffs and landings from unimproved landing surfaces are promoted by Viking as valuable to special-mission operators. The airframe can also be equipped with mission equipment such as a 360-deg. digital color radar system, crew observation station, electro-optical and infrared imaging turret, extended-range fuel tanks and lavatory. Commonalities with commercially utilized versions of this DHC-6 variant include its versatility—with the airplane able to be “quickly redeployed and adapted” between missions such as medevac, SAR, surveillance and transportation—as well as the fact that the Guardian 400 can be equipped with the previously discussed types of landing gear. The endurance is noted as being “up to 10 hr.,” while the airframe is also capable of carrying a “larger payload for [an] extended range.”

Program Status/Operators

From the first delivery to Trans Australian Airlines on July 29, 1966, the production of the DHC-6 Series 100/110, 200/210 and 300/310/320 continued until 1988, with 844 Twin Otters being produced during the 22-year production run of those series of the type. When Viking subsequently restarted production of the DHC-6 type, they did so at an aircraft assembly facility located in Calgary, Alberta.

References

  • AWIN Article Archives
  • Honeywell, Pratt & Whitney and Viking Commercial Materials
  • EASA TCDS (DHC-6)
  • FAA TCDS (PT6A)
  • Transport Canada TCDS (DHC-6) 
Channel
Business Aviation
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ALL
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10
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Program Profile ID
10430