Resolving the problem with the guns had prevented the aircraft from undergoing its State acceptance trials in July 1953 as stipulated and a special commission was appointed to conduct the trials on 31 December 1953. After the manufacturer's trials were successfully concluded in January 1954 the aircraft was turned over and the State acceptance trials lasted from 21 January — 15 March 1954. The tests were generally successful with the Il-40 proving to be easy to fly, maneuverable enough to be a handful for the MiG-15bis and MiG-17 fighters opposing it and considerably superior to the piston-engined Ilyushin Il-10M ground-attack aircraft then in service. However flight tests did reveal blast gas ingestion when firing in a sideslip by the engine on the side opposite the sideslip. Several solutions were evaluated to cure the problem, but Ilyushin pushed for the more radical solution of extending the air intakes for the engines all the way to the nose of the aircraft and moving the guns to the bottom of the nose, behind the air intakes.