On 6 December 1978, Embraer was officially awarded a contract to produce two prototypes and two airframes for fatigue tests. The specifications were concluded in February 1979, and the main differences from the EMB-311 were the more powerful PT6A-25C engine, raised rear cockpit, and the addition of ejection seats. Eventually, the original specifications underwent a major modification, including a smaller fuselage with an upright cruciform tail instead of a swept-back tail; a more domed canopy; extended elevators; greater distance between the nosewheel and back wheel; reduction of the wing root; and an increased wingspan, tailplane, and landing gear. By late 1979, a full-scale mock-up was built with a cockpit for the evaluation of flight instruments, and a subscale, radio-controlled research model was designed to evaluate the free-flight characteristics before building a full-scale prototype.