Turkey's rules of engagement were changed long before Tuesday's downing of Russian aircraft when on June 22, 2012 Syria shot down an unarmed Turkish RF-4E aircraft, which was on a training flight to test eastern Mediterranean radars.
The aircraft was downed within the international airspace without any warning, killing two Turkish pilots, according to the Turkish General Staff.
The incident had increased tensions between both sides and the Turkish Foreign Ministry sent a diplomatic note to Syria's Istanbul Consulate General, saying: "It is unacceptable to down a Turkish aircraft without any warning and the responsibility of this attack is on Syria."
Later, on Turkey's request, NATO foreign ministers gathered in December 2012 and agreed to send the Patriot missile defense systems to Turkey.
The U.S., Germany and the Netherlands sent Patriot missile batteries, which were stationed in the provinces of Gaziantep, Adana and Kahramanmaras in early 2013, respectively.
Turkey's revised engagement rules included responding to aerial and ground threats on the border immediately.
After the regulated engagement rules, Turkey responded to Syria's violations. In Oct. 2012, artillery fire by the Syrian side killed five people in Akcakale district of Turkey's southeastern Sanliurfa province. In response, Turkish Armed Forces hit targets in Syria immediately.
In May this year, Turkish jets also shot at a Syrian helicopter when it violated Turkish airspace. Last month, Turkey also downed an unidentified drone when it intruded into Turkish airspace near Syria.
Soon after Russia's airstrikes in Syria began on Sept. 30, two incursions by Russian aircraft into Turkish airspace occurred, one on Oct. 3 and another on Oct. 4. Each time, Turkish F-16 jets intercepted the Russian fighters forcing them to turn back. Russian officials apologized and pledged that no such incident would be repeated. Turkey had also renewed its warning on rules of military rules of engagement, including a military response against violations of Turkish airspace.
On Tuesday, two Turkish F-16 fighter jets on an aerial patrol intercepted an unidentified warplane within rules of engagement when it intruded into Turkish airspace on the Turkey-Syria border.
The intruding aircraft was warned about the violation 10 times within five minutes before it was shot down.
The Russian Defense Ministry later announced that its Russian SU-24 bomber jet had been shot down. It crashed in the Syrian region of Bayirbucak close to Yayladagi district of Turkey's southern Hatay province.
NATO confirmed the accuracy of information shared by Turkey about the violation.