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 , but was overall a larger aircraft . Design and development . When de Havilland Canada began design work on the " King Beaver " ( the Otter ' s original name ) in January 1951 , it was trying to extend the company ' s line of rugged STOL utility transports that had begun with the Beaver . The single - engined , high - wing , propeller - driven DHC - 3 Otter was conceived to be capable of performing the same roles as the Beaver , but was considerably larger , the veritable " one - ton truck " ( in company parlance , the Beaver was the " half - ton truck " ) . Using the same overall configuration as the earlier and highly successful DHC2 Beaver , the new design incorporates a longer fuselage , greater - span wings , a cruciform tail , and is much heavier . Seating in the main cabin is for 10 or 11 , whereas the Beaver can seat six . Power is supplied by a 450 - kW ( 600 hp ) Pratt & Whitney Wasp radial . 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 . The Otter received Canadian certification in November 1952 and entered production shortly thereafter . Operational use . The DHC - 3 / 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 ) . The engine was a Pratt & Whitney R - 1340 ( 1 , 340 cubic inches ) geared engine . The version used in the Otter was geared for lower propeller revolutions and consequently lower airspeed . The electrical system was 28 volts D . C . 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 maneuvers . 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 . It was stood down , and 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 . Modifications . 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 400 lb " upgross " kit which increases the gross weight of the DHC - 3 to 8 , 367 lbs 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 .