Iranian military leaders admit that their air force, despite remarkable efforts to improvise, is in sad shape. There are about fifty modern fighters capable of flying and fighting. Half of these are American F-14s from the 1970s. Although frequently refurbished none have been upgraded much although Iran claims two F-14s have received some modern equipment. Iran has about 30 flyable MiG-29s, all built in the late 1980s and none have received the upgrades most other MiG-29s of that period have received. Russia helped supply components to keep most of the 36 MiG-29s Iran received by 1991 flying. The only notable upgrade was to enable these aircraft to use Iranian made anti-ship missiles. With Chinese help, Iran has kept about fifty of its 1960s vintage F-4 fighter-bombers operational, but as reconnaissance aircraft and bombers. Iran has about fifty of its nearly fifty year old F-5 fighter-bombers flyable. These, like the F-4s, are considered dangerous to fly given their age and improvised maintenance and repairs over the years. The pilots don’t get a lot of time in the air and are this much less capable than the Arab fighter pilots they face, who have modern, well maintained Western warplanes that are regularly upgraded and flown a lot. Iran also has about 60 elderly Russian ground attack aircraft; mainly Su-24s and Su-22s plus a few Su-25s. Iran has tried to create “new” aircraft by heavily modifying F-5s but this has not produced any significant results other than ten aircraft that are flyable but not very capable.
After arch-enemy Saddam Hussein was overthrown in 2003 (by a U.S.-British invasion) Iran felt free to concentrate on refurbishing more of its elderly warplanes. With more money and manpower diverted to this program a lot of the older aircraft were made operational once more. In 2013 Iran announced that ground crews and other technical personnel at an air force base had spent 45,000 manhours to get two Mirage F1 fighters back into flying condition. Iran received 24 of these aircraft from Iraq in 1991, when Saddam ordered most of his combat aircraft to fly to Iran and surrender (rather than be bombed by coalition aircraft). Iran kept all these aircraft but found it difficult to operate them, especially if none were already in the Iranian Air Force. The aircraft did not come with any support or maintenance equipment and especially no spare parts. Over the years, some parts and maintenance equipment were obtained, but in two decades these older aircraft, left outside most of that time, deteriorated. The two Mirages restored did not remain flyable for long. That made it clear that many of these refurbs just were not the effort. Meanwhile, China proved willing and able to supply some parts and electronics that could be used in the American warplanes.
Refurbishing older warplanes meant taking them apart, obtaining (via China, smugglers or local manufacture) new or used parts, replacing the defective ones and then reassembling it all. The two refurbished Mirage F1s managed to fly, but since then little has been heard or seen of them. This sort of thing seems like a useful way to keep ground crews busy when the air force can’t get enough money to let even the flyable aircraft fly much. Fuel and spares cost money, money that Iran does not have. Earlier news stories have mentioned similar refurbishing projects for F-14s, F-5s, F-4s, and MiG-29s which have been more successful, up to a point.
The Iranian problem is that three decades of sanctions have made it impossible to replace obsolete and worn out gear or even maintain the elderly systems they have to rely on. For example, Iran has been having increasing problems keeping its 1970s era F-5s operational. The ones that are still flying tend to crash a lot or not be available for use because of maintenance problems (including spare parts shortages). Spare parts for all U.S. aircraft Iran still uses have been hard to come by. Iran has managed, sort of. Nevertheless, the Iranian Air Force is largely a fraud. It has lots of aircraft that, for the most part, sit there but can't fly because of age and lack of replacement parts. Those that can fly would likely provide target practice for enemy fighters.
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 for even that 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. That was the main reason so many of these are still flying for the Iranian air force, although only about half of those declared flyable are capable of doing so 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 can still put at least 20 F-14s into the air on short notice. The manhours spent on keeping these aircraft flyable is far greater than any other user had to devote to that. Iranian pilots are not very experienced but their aircraft maintainers are, which would be an asset if Iran could obtain modern aircraft.
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 the lack of Iranian money for high-ticket items, not too 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 the 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. Black market spare parts have been available, but the MiG-29 is a notoriously difficult aircraft to maintain, even when you have all the parts you need.
Iran currently has about two hundred fighters and fighter-bombers that are flyable but most of these are good for only about one sortie a day. All of these are subject o breakdowns that can keep them on the ground for days or weeks. 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.
Finally, there is an ideological problem. The IRGC (Iranian Revolutionary Guard Corps), a special force staffed by men loyal to the clerical dictatorship, exist mainly to ensure that the armed forces, especially the air force, remain loyal to the religious dictatorship. The IRGC has blocked Iranian Air Force plans to obtain modern warplanes (as a result of the 2015 treaty that lifted most sanctions) until they had assurances that IRGC personnel would be integrated into the squadrons operating these new aircraft. The air force leaders pointed out that such a policy would interfere with training and combat use of the new aircraft. With the Americans reviving the sanctions and Russia burdened by another set of sanctions imposed after Russian attacked Ukraine in 2014 and threatened other East European nations, it would be very difficult to obtain new warplanes from Russia. China will supply aircraft components but not new aircraft in part because most modern aircraft China builds are illegal copies of Russian designs. China and Russia are still at odds over that but one thing China has apparently agreed to is not exporting the disputed designs.
Thus Iran is stuck with the oldest, least capable fleet of warplanes in the Middle East. No wonder Iran has put so much effort into building ballistic missiles and, eventually, nuclear weapons.