The G.91Y is a derivative of the Fiat G.91; while intended to perform the same roles and baring a strong visual resemblance to one another, the G.91Y was an extensive redesign of its predecessor. The most prominent difference between the two aircraft was that G.91Y was powered by a new twin-engine configuration that replaced the earlier aircraft's single engine arrangement. In combination with weight reduction measures, additional fuel tanks, and a variety of new license-produced avionics, the G.91Y's performance and capabilities differed considerably from the G.91.