De Havilland Canada DHC-3 Otter

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, but is overall a larger aircraft.

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.

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 dropzones 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.

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.

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 Pezetel 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 Otter:Conversions powered by PZL Kalisz ASz-62IR engines.
;Texas Turbines Super Otter:Turbine conversion powered by a Garret TPE331 turboprop engine
;Aerotech Industries Turbine conversion powered by a 900shp Pratt & Whitney Canada PT6A-140A turboprop engin

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 12 Otters (G300 – G311), in service 1961-1973 (serial number: 413, 414, 416, 418, 420, 422, 424, 425, 426, 428, 430, 431).
** 4 aircraft had to be written off, 8 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
* Vancouver Island Air
* Bearskin Airlines (formerly)

;
* Fjellfly
* Varangfly
* Westwing A/S
* Widerøe

;
* Philippine Airlines (formerly)

;
* Talkeetna Air Taxi
* Kenmore Air
* Wings Airways
* Key West Seaplane Adventures
* Northwest Seaplanes

;
* Pacific Island Air

;
* Volcanic Air (Rotorua)

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.
*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.
*On 9 August 2010, a DHC-3T registered to Anchorage-based GCI crashed about north of Dillingham, Alaska, while en route to a private fishing lodge. Five of the nine people on board were killed, including former Alaska Senator Ted Stevens. Surviving passengers included former NASA administrator Sean O'Keefe and his teenage son, both of whom sustained injuries.
*On 23 September 2011, a DHC-3T Turbine Otter floatplane, N361TT, sustained substantial damage during a go-around and subsequent low-altitude maneuver at Heitman Lake, about 5 miles south-southwest of Kodiak, Alaska, killing the pilot and injuring the two passengers. One of the passengers reported that during the go-around, the airplane struck a tree on the shoreline and crashed.
*On 7 July 2013, a DHC-3 Otter registered to Rediske Air, N93PC, crashed on takeoff at Soldotna Airport, Alaska, killing all ten aboard. There were no surviving witnesses and the aircraft did not carry a flight data recorder, but the NTSB was able to reconstruct the aircraft's flight path using a recovered mobile phone video recorded by a passenger. The NTSB attributed the a