Part of the problem was that few Syrian air force leaders (and pilots) were prepared for this kind of war (low level bombing and lots of helicopter flights under fire). Desperate time remand desperate measures, and in the last few months even the MiG-29 fighters have been seen dropping bombs. These are the most modern aircraft Syria has and their pilots were trained to fight Israeli jets, not bomb civilians. But a village or city neighborhood is hard to miss, even for a rookie.
A more costly problem is the lack of flying time in the last decade. Syria could never afford, even with Iranian subsidies, to let their combat pilots fly enough to be really good at it. For the last year, the only flying has been for combat missions. MiG-29 pilots were taught about bombing, if they had no experience in that, on the ground and practiced the weapons release procedure while the aircraft were sitting on the ground. The first actual bomb drop was for real, not practice. This lack of flight time led to operational losses, especially when it came to landing damaged (by enemy action or equipment failure) aircraft. This often led to aircraft loss rather than bringing home a repairable aircraft. A shortage of spare parts often made repairs impossible and has become a major factor in aircraft becoming inoperable after heavy use (which wears out some components).
The Syrian Air Force also suffers from an overabundance of older, well-worn, and poorly maintained aircraft. The best example is their use of the MiG-21. This is a 1950s design and most of the few remaining current users are phasing them out. But because Syria is so poor, their 150 MiG-21s are still the most abundant aircraft in their air force. But only about half of these MiG-21s are flyable. There are also a hundred 1960s era MiG-23s, ten MiG-25s, and 40 MiG-29s. There are also 20 Su-24 and 60 Su-22 ground attack aircraft. The 60 operational L-39 jet trainers were also able to carry some weapons (typical with trainers like this) and were used to attack rebels. There is also a large force of helicopters, the most common being over 240 Mi-8s (including some of the more modern Mi-17 model). There are 120 attack helicopters, half of them Mi-24s (a gunship variant of the Mi-8 and contemporary of the American AH-1), the rest are elderly French Gazelle scout helicopters and Polish Mi-2s. These are mostly used as aerial taxis as they only carry a few weapons and can’t handle much damage.
It wasn’t until about a year ago that the rebels (using army deserters and information collected via the Internet or Islamic radical fighters with experience in Iraq) developed effective anti-aircraft techniques. The most common and successful one was to place multiple machine-guns, including at least one heavy (12.7-23mm) machine-gun, along the route used by helicopters or jets coming in for landing or low level attack. These machine-guns were fired in a coordinated manner and were very effective. This tactic is called “flak trap” and dates back to World War II (or earlier). This tactic works if you can use surprise and one or more concealed, preferably truck mounted, heavy machine-guns.
Syrian Air Force losses have been heavy, with some 400 aircrew dead, captured, or missing. Nearly a hundred fixed wing and over a hundred helicopters have been lost. About half of these aircraft were captured or destroyed on the ground as rebels attacked, and often captured, air bases. The jets (and a few transports) were hit while landing and taking off, and this threat often led to airbases being abandoned, with aircraft incapable (because of damage or lack of spare parts) of flying out being destroyed or just left behind. The rebels have about a dozen flyable helicopters and some helicopter pilots have defected, but there is not really a rebel “air force” just yet.
All Syrian aircraft are showing their age, except for the MiG-29s, which are relatively new. Lack of money has meant few flying hours for air force pilots and not enough money to keep all aircraft flyable even before the revolution began two years ago. Fuel and spare parts are even more expensive now (because of sanctions) and the air force has a hard time dealing with the payroll and the expense of running (and defending) its bases.
The Syrian Air Force has a dismal record, although their primary opponent for over half a century has been Israel. The Assad family has occasionally used the air force against the Syrian people and seemed reluctant at first to unleash hundreds of combat aircraft on civilians. But a year ago that changed, and an air attack was considered successful whether it hit armed rebels or the unarmed civilians that supported him. Several air force defectors reported that pilots were often instructed to go after bakeries (bread is a key element of the Syrian diet) and apartment buildings, in order to maximize the suffering among civilians.
The air force is rapidly disappearing because of combat and operational (accidents and poor maintenance) losses. At this point the government has nothing to lose and simply regards the remaining aircraft as similar to diminishing ammo supplies. Use it or lose it to advancing rebels.