The Iranian Air Force is still recovering from the effects of the 1979 revolution (an embargo on spare parts and new aircraft). A number of its aircraft are in good shape, and remain flyable. One of the reasons is because it had an easier time getting a lot of spare parts than the Iranian Navy did, since aircraft parts tend to be smaller and more common than parts for ships.
The reason for this is easily understood once one looks at the Iranian order of battle. Two of the aircraft in service at the time, the F-4 Phantom and the F-5E Tiger, were in very wide service around the world. Somewhere, someone had parts for these planes that Iran could buy (using its oil money). Iran still has about 40 of each aircraft (roughly enough for three squadrons of each).
Iran's big-ticket purchase in the 1970s was the F-14 Tomcat - making it the only export customer of this powerful interceptor. This force has been kept in service, despite the reported sabotage of Iran's AIM-54 Phoenix missiles by technicians as they were on their way out. The Iranians had a solution for that - they begged, borrowed, and even stole parts to keep the Tomcats flying. To demonstrate this, they sent 25 F-14s on a fly-over of Tehran in 1985. Today, Iran has 50-55 airframes, but can only keep one squadron of Tomcats airborne.
Iran has looked to new sources for aircraft. In the 1990s, in the wake of the collapse of the Berlin Wall and the splintering of the Soviet Union, they began buying from Russia. And then there was the 1991 Gulf War, when Iraqi aircraft (many of which were Russian-built) fled to Iran to avoid American attack, and were not given back. Iran ended up with at least 30 MiG-29s (and probably as many as 62) in three squadrons. Iran also got a fair number of Su-24 Fencers (16-18 of which were from Saddam's regime), that are organized into one squadron.
One of the other things Iran has done has been to jury-rig weapons. Both HAWK and Standard surface-to-air missiles have been rigged onto Iranian aircraft - possibly for anti-radar missions. The Iranians have also rigged the F-4 to carry the Chinese C801 anti-ship missile. The Iranians also have rigged the F-5E to carry the PL-7 and the R-60/AA-8 Aphid air-to-air missiles, in addition to the AIM-9 Sidewinder. One entity that should not be neglected is the Revolutionary Guard. The Revolutionary Guard has a force of Chinese and Russian aircraft (30 J-7 Fishbeds, 18 J-6 Farmers, and 44 Su-20/22 Fitters). This force is divided into five squadrons. This force has quantity, but these are very old designs.
Iran's Air Force is held together by ingenuity a lot of scrounging, and they have also been upgrading their force with modern Russian aircraft. Iranian ingenuity has allowed them to keep their air force as a viable force. This is a force that can be extremely easy to underestimate, at one's own peril. - Harold C. Hutchison (firstname.lastname@example.org)