The de Havilland Canada DHC-3 Otter is a single-engined, high-wing, propeller-driven, short take-off and landing (STOL) aircraft developed by de Havilland Canada. It was conceived to be capable of performing the same roles as the earlier and highly successful Beaver, including as a bush plane, while also being a larger aircraft. The type certificate of the aircraft is now owned by the De Havilland Canada founded in 2019.
Design and development The rugged single-engined, high-wing, propeller-driven DHC-3 Otter was conceived in January 1951 by de Havilland Canada as a larger, more powerful version of its highly successful DHC2 Beaver STOL utility transport. Dubbed the "King Beaver" during design, it would be the veritable "one-ton truck" to the Beaver's "half-ton" role.Rossiter 1998, p. 55.
The Otter received Canadian certification in November 1952 and entered production shortly thereafter. Using the same overall configuration as the Beaver, the new, much heavier design incorporated a longer fuselage, greater-span wing, and cruciform tail. Seating in the main cabin expanded from six to 10 or 11. Power was supplied by a 450-kW (600 hp) Pratt & Whitney R-1340 geared radial. The version used in the Otter was geared for lower propeller revolutions and consequently lower airspeed. The electrical system was 28 volts D.C.
Like the Beaver, the Otter can be fitted with skis or floats. The Otter served as the basis for the very successful Twin Otter, which features two wing-mounted Pratt & Whitney Canada PT6 turboprops. A total of 466 Otters were manufactured.
Operational use
The DHC-3/CC-123/CSR-123 Otter was used until 1980 by the Royal Canadian Air Force and its successor, the Air Command of the Canadian Forces. It was used in Search and Rescue, as the "CSR" denotes Canadian Search (and) Rescue (type 123) and as a light utility transport, "CC" denoting Canadian Cargo. During the Suez Crisis, the Canadian government decided to provide assistance to the United Nations Emergency Force and the Royal Canadian Navy carrier carried 4 Otters from Halifax to Port Said in Egypt early in 1957, with all four flying off unassisted while the ship was at anchor. This was the only occasion when RCAF fixed wing aircraft operated from a Canadian warship. It was also operated on EDO floats on water and skis for winter operations on snow. The EDO floats also had wheels for use on runways (amphibious). It was used as army support dropping supplies by parachute, and also non-parachute low-speed, low-altitude air drops, to support the Canadian Army on manoeuvres. In the end it was operated by the Primary Air Reserve in Montreal, Toronto, Edmonton and Winnipeg, with approximately 10 aircraft at each base, as well as by the RSU (Regular (Forces) Support Units) at those bases. It was usually flown with a single pilot (Commissioned Officer) in the left seat and a Technical Air Crewman (NCO) in the right seat. The Kiowa helicopter replaced it in Air Reserve squadrons.
Although the Otter found ready acceptance in bush airlines, as in a similar scenario to the DHC-2 Beaver, the United States Army soon became the largest operator of the aircraft (184 delivered as the U-1A Otter). Other military users included Australia, Canada, and India, but the primary role of the aircraft as a rugged bush plane continues to this day.
An Otter crossed the South Pole in 1957 (see Commonwealth Trans-Antarctic Expedition). The Otter is also popular in the skydiving community and can be found in many drop zones throughout the world.
Otters were used by Qantas from 1958 to 1960 in Papua New Guinea. The Qantas aircraft were then transferred to Trans Australian Airlines (TAA), a major Australian domestic airline, which operated the Otters in Papua New Guinea until 1966 when they were withdrawn from use. TAA was merged with Qantas in 1990.
Modifications The most extensively modified Otter was RCAF Otter 3682. After initial service as a standard Search and Rescue aircraft it was used to explore the aerodynamic aspects of STOL. In 1958, it was fitted with flaps so outsized that, with their 45 degree droop, it became known as the Batwing Otter. In addition, its tail-wheel undercarriage was replaced with a high energy-absorption 4-wheel arrangement and a very high vertical tail. The next modification replaced the flaps with fully retractable flaps suitable for cruising flight and high drag was obtained with reverse thrust from a J85 turbojet installed in the fuselage behind the cockpit. The third configuration looked a lot like the future Twin Otter and was the first twin-PT6 fixed-wing installation to fly in May 1963 (A twin PT6-engined helicopter, the Kaman K-1125, had flown in April 1963). The piston engine in the nose was replaced with wing-mounted engines to blow over the flaps.https://www.flightglobal.com/pdfarchive/view/1963/1963%20-%200073.html?search=january%20stol%20otter Power – The Pratt & Whitney Canada Story, Kenneth H. Sullivan and Larry Milberry, CANAV Books 1989, , p. 147The Universal Airplanes – Otter & Twin Otter, Sean Rossiter 1998, Douglas & McIntyre, , pp. 13–31
Stolairus Aviation of Kelowna, BC, has developed several modifications for the DHC-3 including a STOL Kit, which modifies the wing with a contoured leading edge and drooped wingtips for increased performance. Stolairus has also developed a "upgross" kit which increases the gross weight of the DHC-3 to on floats."DHC-3 Otter." Stolairus, Retrieved: 2 February 2012.
Some aircraft were converted to turbine power using a PT6A, Walter 601 (manufactured in the Czech Republic), or Garrett/Honeywell TPE331-10, by Texas Turbine Conversions. The Walter M601E-11 Turbine Engine conversion is manufactured and installed by Stolairus Aviation.
A Polish PZL radial engine has also been fitted. Re-engined aircraft have been offered since the 1980s by Airtech Canada as the DHC-3/1000 using current-production 1,000 hp (745 kW) PZL ASz-62 IR radials.Taylor 1988 p. 17.
Variants DHC-3 Otter Single-engined STOL utility transport aircraft. CSR-123 Otter STOL utility transport aircraft for the Royal Canadian Air Force. YU-1 Otter Six test and evaluation aircraft for the U.S. Army. U-1A Otter STOL utility transport aircraft for the U.S. Army. UC-1 Otter STOL utility transport aircraft for the United States Navy. Later redesignated U-1B Otter in 1962. Otters fitted with either Pratt & Whitney Canada PT6A-27 or Pratt & Whitney Canada PT6A-34 turboprop engine. Airtech Canada DHC-3/1000 OtterConversions powered by PZL Kalisz ASz-62IR engines. Texas Turbines Super OtterTurbine conversion powered by a Garret TPE331 turboprop engine Aerotech IndustriesTurbine conversion powered by a 900shp Pratt & Whitney Canada PT6A-140A turboprop engine.
Military operators
Argentine Air Force: Former operator
Royal Australian Air Force: Two Otters (RAAF serial A100-1 and 2) were in service with the RAAF from 1961 to 1967. The aircraft were used for passenger and freight transport duties at the Weapons Research Establishment, Woomera, South Australia. No. 1 Air Trials Unit
Bangladesh Air Force: Former operator
Burma Air Force
Royal Canadian Air Force
Chilean Air Force
Air Surveillance Service
Ethiopian Air Force
Ghana Air Force – acquired twelve Otters (G300 – G311), in service 1961-1973 (serial number: 413, 414, 416, 418, 420, 422, 424, 425, 426, 428, 430, 431). Four aircraft had to be written off, eight aircraft were sold in 1973. G300 (s/n 413) crashed on 21 June 1968 in the jungle in the Brong Ahafo region of Ghana and was destroyed. G301 (s/n 414) crashed on 31 August 1961 at Kintampo in the Brong Ahafo region of Ghana and was destroyed. G302 (s/n 416) crashed on the beach near Takoradi on a date unknown and was destroyed. It was on floats at the time, on a training detail. G308 (s/n 426) was written off in service.
Indian Air Force
Indonesian Air Force
Khmer Air Force: Former operator
Royal New Zealand Air Force
Nicaraguan Air Force
Royal Norwegian Air Force
Panamanian Public Forces
Paraguayan Air Force: One DHC-3 donated by Argentina.
Tanzanian Air Force
Royal Air Force
United States Air Force United States Army United States Navy Otter NU-1B is the oldest aircraft in the U.S. Navy, in service at the U.S. Naval Test Pilot School, Patuxent River, Md.
Civil operators
Qantas Trans Australia Airlines
Royal Canadian Mounted Police Lamb Air Harbour Air Osprey Wings Ltd Provincial Airlines Air Saguenay (formerly) Air Tunilik Air Tindi Vancouver Island Air Bearskin Airlines (formerly)
Pacific Island Air
Merpati Nusantara Airlines (formerly)
Volcanic Air (Rotorua)
Fjellfly Varangfly Westwing A/S Widerøe
Philippine Airlines (formerly)
Talkeetna Air Taxi Kenmore Air Wings Airways Key West Seaplane Adventures Northwest Seaplanes
Accidents As of June 2019, there have been 119 incidents and accidents involving the DHC-3 resulting in 242 deaths. Listed below are a select few of the most notable ones.
In 1956, two military Otters broke up in mid-air. One had taken off from Downsview and the other from Goose Bay. The Otter requires immediate use of elevator trim to counteract the strong change in pitch caused by the retraction or extension of the flaps. Investigators found that metal contamination in a hydraulic valve allowed the flaps to rapidly retract with the tailplane still fully trimmed, and the consequent nose drop was severe enough to cause structural failure. A filter was added to the flap hydraulic system and an interconnection added between the flaps and tailplane to maintain proper trim as the flaps are operated.Air Crash – The Clues in the Wreckage, Fred Jones 1985, Roobert Hale Ltd., , pp. 104–112 On 20 May 1964, Philippines Airlines Flight F26, a DHC-3 Otter, PI-C51, crashed into a hill when flying at VFR at Subico Point, killing all 11 on board. On 24 March 1986, a DHC-3 Otter floatplane, C-FAGM, of Labrador Airways, crashed while returning to Goose Bay Airport from a trip to Snegamook Lake to retrieve a group of partridge hunters. On the return trip, the aircraft encountered engine trouble. The pilot, Howard Mercer, who was the president of Goose Bay Air Services, called dispatch to report the engine running rough. As the aircraft neared Nipishish Lake, 47 miles north of Goose Bay, the pilot reported experiencing engine problems again, and that he would follow the Crooked River towards the airport as a precautionary measure for if an emergency landing was needed. Three minutes later, the pilot called dispatch to inform them he would be making an emergency landing on the river due to a smoke odour in the cockpit. The aircraft never made it. Due to whiteout conditions and the frozen surface of the river, when the pilot flew close to the ground to land, the wing struck the ground and the aircraft broke apart and was subsequently engulfed in flames. Three passengers and the pilot were killed, while one passenger survived the crash with serious injuries. On 22 June 1994, a DHC-3 Otter floatplane, N13GA, registered to and operated by Wings of Alaska of Juneau, Alaska, crashed into the Taku Inlet, 12 miles east of Juneau. The air taxi flight had departed the Taku Lodge located on the Taku River bound for the Juneau downtown dock. Instrument meteorological conditions prevailed at the time of the accident. Six passengers were killed, one passenger was missing and presumed dead, and the pilot and three passengers received serious injuries. The National Transportation Safety Board (NTSB) attributed the accident to continued VFR into IMC and the pilot's consequent failure to maintain altitude above the water surface.