Snctions or not, no outside entity forces Iran to operate whatever aircraft they have in whatever condition Iran chooses to fly it's aircraft. Iran has many Russian aircraft with plenty of Russian spare parts available, yet Iran crashes many Russian aircraft. Iran has access to some European built aircraft and spares as well. The U.S. over the past 30 years, in an effort to improve aviation safety of Iranian civil aviation has supplied/sold the Iranian regime with some spare parts for it's aircraft.