In the early stages of development, various different powerplants and engine configurations were studied to power the type; both twin-engine and single-engine approaches were considered. The use of US-sourced engines had been promptly discounted to avoid any potential restrictions on export sales of the overall aircraft. Amongst the engines examined were the Turbo-Union RB199 (as used by the larger Panavia Tornado), the Rolls-Royce Turbomeca Adour, Rolls-Royce Viper, and the Rolls-Royce Spey engine. In 1978, the Spey 807 model, which featured several additional improvements, was selected to power the new aircraft.