The Il-40 first flew on 7 March 1953, and flight tests revealed no serious shortcomings in the air. The operational CG was too far aft, but this was only a minor problem when landing, taking off and taxiing, especially when coupled with the rather short wheelbase. The biggest problem proved to be the guns and their effect on the engines. During the first aerial test of the cannons at the end of March 1953 the muzzle flash temporarily blinded the pilot and both engines flamed out. The pilot was able to restart the engines and returned safely, but Sergey Ilyushin immediately started an investigation into the cause of the engine problems. Ground tests with high-speed cameras revealed that none of the muzzle brakes or blast suppressors tested made any difference; the engines would hiccup even if only a single gun fired just five to ten rounds.