Question: The Agderfly AS flight school in Norway utilized which type of twin-turboprop STOL utility aircraft between 1989 and 1992?

Context paragraphs:
Pilatus PC-6 Porter: The Pilatus PC-6 Porter is a single-engined STOL utility aircraft designed by Pilatus Aircraft of Switzerland.  First flown in 1959, the PC-6 continues in production at Pilatus Flugzeugwerke in Stans, Switzerland.  It has been built in both piston engine- and turboprop-powered versions and was produced under licence for a time by Fairchild Hiller in the United States.

Antonov An-14: The Antonov An-14 Pchelka (Russian: «Пчелка» , "Little Bee", (NATO reporting name Clod) is a Soviet utility aircraft which was first flown on 15 March 1958.  It was a twin-engined light STOL utility transport, with two 300 hp Ivchenko AI-14RF radial piston engines. Serial production started in 1966, and about 300 examples were built by the time production ended in 1972.  The An-14 failed to replace the more successful An-2 biplane, which was manufactured until 1990, (the An-2 is still manufactured on special order).  The An-14's successor, the An-28 with turboprop engines, is still manufactured at PZL Mielec factories in Poland, under the names PZL M28 Skytruck and PZL M28B Bryza.

Dornier Do 28: The type designation Dornier Do 28 comprises two different twin-engine STOL utility aircraft, manufactured by Dornier Flugzeugbau GmbH.

Agderfly: Agderfly AS was a flight school and airline based in Kristiansand, Norway, which operated from 1966 to 2004.  Originally based in Froland, since 1969 it operated out of Kristiansand Airport, Kjevik.  Agderfly was owned by Ola Rustenberg, who was also chief instructor.  From 1989 to 1992 the company was split into three, with one part responsible for scheduled services.  It operated two Dornier Do 228 and flew services from Kristiansand to Gothenburg, Billund and Bremen.

Dominion Skytrader: The Dominion Skytrader was a Canadian prototype STOL utility aircraft, originally designed by the Dominion Aircraft Corporation in Vancouver, British Columbia, but built in the United States in the early 1970s.  Attempts to market the aircraft continued until the late 1980s, but proved fruitless.

Dornier Do 228: The Dornier Do 228 is a twin-turboprop STOL utility aircraft, manufactured by Dornier GmbH (later DASA Dornier, Fairchild-Dornier) from 1981 until 1998.  In 1983, Hindustan Aeronautics (HAL) bought a production licence and manufactured 125 aircraft.  In Oberpfaffenhofen, Germany, 245 were built, and 125 in Kanpur, India.  In July 2017, 63 aircraft were in airline service.

Helio Aircraft Company: The Koppen-Bollinger Aircraft Corporation was founded by Otto Koppen and Lynn Bollinger in Massachusetts in 1948 to develop a light STOL utility aircraft.  It was renamed the Helio Aircraft Corporation by the time manufacture of the Helio Courier, commenced in the early 1950s at a plant in Pittsburg, Kansas.

Dornier Do 27: The Dornier Do 27 was a German single-engine STOL utility aircraft, manufactured by Dornier GmbH (later DASA Dornier, Fairchild-Dornier).  Configuration was a classic high-wing, "tail-dragger" aircraft with fixed landing gear.

AAC Angel: The Angel Aircraft Corporation Model 44 Angel is a twin-engine STOL utility aircraft produced in the United States since the mid-1990s.  Designed by Carl Mortenson and The King's Engineering Fellowship to be well-suited for missionary work from remote locations around the world, it is a low-wing cantilever monoplane with a retractable tricycle undercarriage and eight seats.  The design is largely conventional, with the exception that the engine nacelles are mounted on top of the wings in a pusher configuration.  Construction is aluminium throughout the airframe.

Aero L-60 Brigadýr: The Aero L-60 Brigadýr (Czech: "Brigadier" ) was a small, high-wing propeller-driven Czechoslovakian STOL utility aircraft developed for both civil and military use.  A prototype, designated XL-60, with Argus As 10C engine, first flew on December 24, 1953, but it was not successful.  The plane was thoroughly redesigned and the second improved prototype, with M-208B flat-six engine, flew on June 8, 1954.  The aircraft's configuration bears a strong resemblance to the Fieseler Fi 156 "Storch" licence-produced in Czechoslovakia during and after World War II (as K-65 Čáp), and which this aircraft was intended to replace.  By the end of production in 1960, 273 had been built by Aero, including an improved version, the L-160 with an all-metal tail.

Supporting paragraphs: Agderfly Dornier Do 228
Answer: Dornier Do 228