James Joyner at the Atlantic Council of the United States has written a blog post explaining why NATO will not use the Syrian downing of a Turkish jet as an Article V casus belli. it seems to NATO Monitor that this section of his post is particularly noteworthy:
Instead, the operative word that almost certainly disqualifies this incident from an Article 5 response is "attack." Turkey was engaged in aggressive action along its border with Syria during a particularly tense situation and flew into Syrian airspace. While shooting down the plane was almost certainly an overreaction--the Assad government has said as much--it's hardly an "attack."
Ultimately, like the "high crimes and misdemeanor" threshold for impeachment set forth by the US Constitution, it's a judgment call. In the former case, the House of Representatives makes the call; in the latter, it's the North Atlantic Council.
But it's virtually inconceivable that the NAC would deem this to be a qualifying "attack." First, Article 5 couches the response in terms of "the right of individual or collective self-defence recognised by Article 51 of the Charter of the United Nations." An overly aggressive defensive action by Syria--especially a one-off--would not seem to qualify. While the Turkish pilot would certainly have been within his rights to use deadly force to protect himself, a retaliatory strike at this juncture by Turkey--much less its NATO allies--would be in violation of the UN Charter.
Second, borrowing language from Article 51, Article 5 specifies the rationale for the use of force as "to restore and maintain the security of the North Atlantic area." Given that the incident is already contained--that is, not likely to be followed by any sort of follow-on action by Syria absent further provocation--said security already exists. Indeed, a NATO or Turkish response would make the area more, not less, secure.The whole piece is worth reading and the analysis seems very sound, especially given the quiet reaction to the incident from NATO foreign ministries to date.