"Under article 4, any ally can request consultations whenever, in the opinion of any of them, their territorial integrity, political independence or security is threatened," Lungescu said. The North Atlantic Council — the ambassadors of the 28 NATO countries — will decide whether to respond, she said.
The last time article 4 was invoked was nine years ago — also by Turkey — after tensions with neighboring Iraq escalated. However, that case did not lead to the invocation of article 5, which declares that an attack against any single NATO country shall be considered as an attack against them all.
Despite some opposition leaders' calls for Western military intervention in Syria, the United States and allies have been hesitant to get involved in what could prove a protracted conflict, preferring the diplomatic route. Syrian allies Russia and China have already shielded Syria from U.N. sanctions and stridently oppose any military intervention.
It's unlikely the downing of the Turkish plane will change those calculations, despite Ankara's appeal for the NATO meeting.
In October 1989, two Syrian MiG-21s violated Turkish air space and shot down a Turkish plane on a geographical survey mission, killing all five crew members. Syria at the time promised to severely punish the pilots, who disregarded Turkish orders not to enter Turkish airspace.