This is a twin-engined version of the successful AS.350 with the Starflex rotor system and first flew in 1979. Aimed at the large IFR-capable civilian market, the AS.355 was fitted with twin Allison turboshaft engines. After several modifications the latest civilian variant the AS.355F2 is fitted with twin Allison turbines developing around 315kW and new wider composite blades and remoulded engine intakes for anti-icing protection. The French Air Force operate the AS.355N in the surveillance role and later models are fitted with Turbomeca TM319 turbines.

P.Allen "The Helicopter", 1996

The need for a light twin-turbine helicopter, particularly in America, led Aerospatiale to develop a bigger version of the Ecureuil — Ecureuil II (or Twinstar) — powered by two 420shp Allison 250-C20F. It made its first flight on 27 September 1979 followed by the second prototype on 13 November. After 122 hours' flight testing, production went ahead at a rate of between five and seven helicopters a month, rising to 20-24 in 1981.