An Iranian Air Force Su-24 bomber recently crashed. Last year, a U.S. built Iranian F-5 fighter crashed during a training exercise. One could understand these losses, both aircraft are old (the F-5 was bought over three decades ago). Spare parts for U.S. aircraft have been hard to come by, but Iran has managed, sort of. Nevertheless, the Iranian Air Force is largely a fraud. It's lots of aircraft that sit there, but can't fly.
The big problem is not the loss of elderly U.S. and Russian warplanes, but the many other older transports and airliners that have been going down. Since 2003, there have been at least a dozen crashes, leaving about 700 passengers and crew dead. Most of the downed aircraft were not American. Many of the lost aircraft were Russian, a nation that has no problems selling Iran aircraft parts. So what's the problem? Simple. Iranian aircraft maintenance sucks. That's because a lousy economy and a really bothersome lifestyle police have caused many technically skilled people to flee the country. Plenty of competent Iranian aircraft mechanics and engineers in southern California, not so many in Iran.
To make matters worse, anything involving aviation in Iran, gets a lot of attention from the secret police. Anyone of questionable loyalty to the clerical theocracy (that runs the country) is not suitable for key jobs (be they technical or managerial.) As a result, many organizations in Iran, especially government controlled ones, are poorly run. That can be fatal for passengers in Iranian aircraft. There are plenty of dead bodies and aircraft wreckage to prove it. It also says a lot about the readiness and capabilities of the ships and aircraft of the Iranian armed forces.
The Iranian Air Force is still recovering from the effects of the 1979 revolution (an embargo on spare parts and new aircraft). Despite that, many Iranian warplanes remain flyable, but only for short periods. The main reason is an extensive smuggling operation, to obtain spare parts. Two of their aircraft, the U.S. F-4D and F-5E Tiger, were widely used around the world. Somewhere, someone had parts for these planes that Iran could buy. There are still about 40 of each still in service, with about half of them flyable at any time.
This was less the case with Iran's most expensive warplane, the U.S. F-14 Tomcat. Iran was the only export customer of this aircraft. The F-14s have been kept flyable, despite the rumored sabotage of Iran's AIM-54 Phoenix missiles by U.S. technicians as they were leaving. To demonstrate this, they sent 25 F-14s on a fly-over of Tehran in 1985. Today, Iran has about 20 F-14s, with less than half of them flyable.
Iran has sought to buy new for aircraft. In the 1990s, with the end of the Cold War, and the collapse of the Soviet Union, they sought to buy from Russia. Despite the low prices, a combination of Western pressure (to not sell) and lack of Iranian money for high-ticket items, not that many aircraft were obtained. One unforeseen opportunity was the 1991 Gulf War. Many Iraqi aircraft (most of them Russian-built) fled to Iran to avoid American attack. The Iranians never returned them. Iran ended up with up to 60 MiG-29s. There were also 18 Su-24s, a force that was expanded by more purchases from Russia.
Iran currently has 220 fighters and fighter bombers, but only about have can be put into action. The chronic shortage of spare parts, limits the number of hours the aircraft can be flown. This means pilots lack good flying skills. The poor maintenance and untrained pilots leads to more accidents.