A single Rolls-Royce Spey turbofan engine serves as the AMX's powerplant. During the aircraft's development, the Spey was heavier and less modern than some of the available alternatives, but it was considered to be reliable, relatively cheap and was free of export restrictions that would be imposed by using American engines. The Spey engine also enabled for the use of a simplified round-lipped inlet design. The rear fuselage is detachable in order to gain access to the engine. Separate consortia in both Brazil and Italy manufactured the Spey for the AMX. Unusual for a strike aircraft of the era, no attempt was made to develop the aircraft to fly at supersonic speeds.