From the expert himself.
No one has more experience with situations such as what transpired over the Syrian/Turkish airspace than this fella, so listen to what he has to say.

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Lt. General Tom McInerney is an expert on handling threats from fighter jets.

McInerney served as:

Commander of the North American Aerospace Defense Command (Norad) – the military agency responsible for protecting the United States and Canada from foreign jet attacks – for the Alaska region

Commander of the Alaskan Air Command

Commander of 11th Air Force in Alaska

Commander of the 3rd Tactical Fighter Wing, Clark Air Base, Philippines

Commander of the 313th Air Division, Kadena Air Base, Japan

Commander of 3rd Air Force, Royal Air Force Station Mildenhall, England

Vice Chief of Staff of the U.S. Air Force

A command pilot with more than 4,100 flying hours, including 407 combat missions

In his role as Norad commander for Alaska, McInerney dealt with more Russian fighter jet incursions (which he calls “bear penetrations”) than anyone else in the world.

So McInerney knows how to tell innocent from hostile incursions by foreign fighter jets, standard rules of engagement of foreign fighter jets, how to read radar tracks, and the other things he would need to know to form an informed opinion about the shootdown of a foreign jet.

Yesterday, McInerney told Fox News – much to the surprise of the reporter interviewing him – that assuming the Turkish version of the flight path of the Russian jet is accurate, Russia wasn’t threatening Turkey, and that Turkey’s shoot down of the Russian jet “had to be pre-planned”, as the jet wasn’t in Turkish air space long enough for anything other than a premeditated attack to have brought it down:

http://video.foxnews.com/v/4630118119001/radar-track-shows-russia-jets-path-over-turkish-territory/?#sp=show-clips

Remember this?

Erdogan criticized Syria harshly on Tuesday for shooting down the Turkish fighter jet, saying: "Even if the plane was in their airspace for a few seconds, that is no excuse to attack."
http://www.cnn.com/2012/06/26/world/meast/turkey-syria-plane/