Rules have changed..
According to Elijah J. Magnier, in his article «New Rules of Engagement on the Battlefield and in the Diplomatic Arena», published in the blog «Fort Russ», citing a source in the command structure of the coalition factions in Syria (Syrian troops, Russia, Iran "Hezbollah" movement), Russia allegedly set new rules of conduct in the area of the Syrian-Turkish border, and established its control over the Syrian Air Force and army. Syrian Air Force received a clear indication to shoot down Turkish jets in case of violation of the border.
According to a source, the government of Hafez al-Assad has entered into an agreement with Turkey in 1998 that the Syrian aircraft will not come near to the border closer than 15 km. Interestingly, when it was signed under the threat of invasion by 10,000 Turkish soldiers Syria was forced to expel Kurdish leader Abdullah Ocalan. The agreement also provided for the non-deployment of Syrian army units near the border, which can only patrol guards and individual officers.