It’s difficult to train pilots.
Here's What You Need To Remember: It’s possible, Cooper wrote, that the SyAAF overhauled the surviving planes and returned them to regular service. The Syrian air arm has made a concerted effort to upgrade dozens of surviving L-39s, subsequently deploying them for nighttime air raids
Between 2013 and 2017 a small number of L-39 light attack jets at a Syrian air force base east of Aleppo changed hands several times. Syrian rebels captured them from the Syrian air force. Then Islamic State militants seized the planes from the rebels. Finally, forces loyal to the Syrian regime recaptured the L-39s.