The design of the AS355N is based on the AS350 helicopter. The two helicopters use the same cabin, fuselage and rotor system. The primary difference is that the AS355N, with its two engines, caters to those operators that for regulatory or other safety reasons cannot use a single-engine helicopter, or require Category A single-engine takeoff performance. In addition, the AS355N has the dual electrical and hydraulic systems required for IFR certification.
Design of the AS355 series of light twin-engine helicopters was started in the late 1970s by the helicopter division of French aircraft manufacturer, Aerospatiale. Aerospatiale was formed in the early 1970s by combining most of the French government-owned aerospace companies, including Sud Aviation, which had been responsible for helicopter design and production. In the 1990s, the helicopter division of Aerospatiale was merged with the German MBB helicopter company to form Eurocopter. Today, Eurocopter is a division of EADS, a multinational European aerospace giant.
The AS355 built on the innovations introduced with the AS350, including the use of composites for the cabin structure, the rotor head as well as the blades. The AS355 uses the same wide, unobstructed cabin as used on the AS350. The standard seating configuration has a pilot and one or two passengers up front and a four-place bench in the back. Alternatively, two litters can be placed longitudinally on the left side of the cabin, one on top the other. The helicopter is also approved for external lift work.
The name “Ecureuil 2” is used in the French-speaking world. The British call this helicopter the “Twin Squirrel”. The name TwinStar, or just AS355, is used in the U.S. and elsewhere.
The drivetrain for the AS355N uses two Turbomeca Arrius 1A engines and a three-bladed composite rotor head and blades. The rotor head, rotor blades and tail rotor are the same as used on the AS350BA, B1, B2 and B3
The original AS355 had its first flight in 1979. The AS355N was certificated in the U.S. in 1992 and was produced from 1992 to 2006.
The AS355NP was introduced in 2006. It has upgraded Arrius 1A1 engines and better climb performance.