offered various Heron modification kits, mainly related to replacing the engines, which greatly enhanced takeoff and top speed capabilities. Riley Aircraft replaced the Gipsy Queens with horizontally-opposed Lycoming IO-540 engines. One U.S. airline that carried out Riley-type conversions at their Opa Locka Airport Florida engineering facility was Prinair, of Puerto Rico, which replaced the Gipsy Queens with Continental IO-520 engines. Prinair also considerably stretched Heron 2 N574PR to allow extra passengers to be carried. Connellan Airways also converted its Herons, using Riley kits. When available aircraft reached the end of their service lives, the engine conversions gave the elderly airliner a new lease of life as a number of examples were converted in the 1970s and 1980s including N415SA, a Riley Heron still flying in Sweden as of 20 May 2012 and a Riley Turbo Skyliner, tail number N600PR currently registered in the United States (this example appeared in the 1986 movie Club Paradise). The most radical modification of the basic Heron airframe was the Saunders ST-27/-28, that basically changed the configuration as well as the "look" of the whole aircraft with two powerful turboprop engines replacing the lethargic four-engine arrangement, a stretched fuselage, the shape of the windows changed and the wingtips squared instead of rounded. Variants Heron 1: Four-engined light transport aircraft. Fitted with fixed landing gear. Heron 1B: This model had an increased takeoff weight of . Heron 2: Four-engined light transport aircraft. Fitted with retractable landing gear. Heron 2A: This designation was given to a single Heron 2, which was sold to a civil customer in the US. Heron 2B: This model had the same increased takeoff weight as the Heron 1B. Heron 2C: Redesignation of the Heron 2Bs, which could be fitted with optional fully feathering propellers. Heron 2D: Four-engined light transport aircraft. This model had an increased takeoff weight of . Heron 2E: VIP transport aircraft. One custom-built aircraft. Heron C.Mk 3: VIP transport version for the Queen's Flight, Royal Air Force (RAF). Two built. Heron C.Mk 4: VIP transport aircraft for Queen's Flight, RAF. One built. Sea Heron C.Mk 20: Transport and communications aircraft for the Royal Navy. Three ex-civil Heron 2s and two Heron 2Bs were acquired by the Royal Navy in 1961. Riley Turbo Skyliner: Re-engined aircraft. A number of Herons were fitted with Lycoming IO-540 flat-six piston engines. The modifications were carried out by the Riley Turbostream Corporation of the