An American aircraft broker, Marc Knapp, was recently indicted by U.S. prosecutors for trying to sell a privately owned F-5 jet fighter to Iran. Knapp wanted $3.6 million from federal agents pretending to represent Iran. Such sales are illegal, and could result in a 40 year prison sentence and a $2 million fine. He'll probably get 2-5 years. The wealthy owner of the F-5 was not involved, he had merely put his privately owned (and demilitarized) F-5 up for sale. Knapp originally attracted government attention when he offered to sell an F-14 ejection seat for $29,000. The U.S. has been destroying its retired F-14s, rather than putting them into storage, to prevent any spare parts from getting to Iran (the only foreign buyer of F-14s, in the 1970s). But some components are still out there. The potential buyer, a federal agent operating undercover as an Iranian purchasing agent, warned Knapp that they had to be careful because this was illegal. Knapp was unconcerned, and it went downhill from there. Knapp offered F-4 and F-14 maintenance manuals for sale as well, and, eventually, the F-5. For this, Knapp was to receive a commission of $500,000. Iran pays well for hard-to-get aircraft and spare parts. There are still lots of F-5s in service, or storage, and Iranian arms smugglers are always seeking to buy F-5 related gear.
Iran has been having increasing problems keeping its 1970s era F-5s flying. For example, two years ago, an Iranian F-5 fighter crashed during a training exercise, and many more rarely get off the ground. 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, because of age and lack of replacement parts.
The Iranian Air Force is still recovering from the effects of the 1979 revolution (which led to 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, that obtains 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 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. Some 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 foreign 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 half 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.