







Was a Russian Su-24 strike bomber over Turkish airspace earlier today when it was shot down by a Turkish F-16 fighter, as the Turkish government claimed? Or did it, as the Russians have claimed, fly in Syrian airspace and never cross the Turkish border? The Turkish and Russian governments have published conflicting evidence on the plane's location as accusations fly between the two sides. But it's entirely possible both sides are right—based on different data sources.

With precision satellite navigation and radar systems available to both sides, one might think that it would be relatively simple to both know where the border was and avoid it or know for certain which side of the border the plane was on when it was shot down. But the Russians have published their own version of navigational tracking data that shows the Su-24 flying south of a part of the Turkish border that juts southward into Syria. The Turks claim that the jet, while clearly not mounting an attack against Turkey, was over a mile into Turkish airspace and had been repeatedly warned that it was on a course that would cross the border.

But given the Russian aircraft was only in Turkish airspace for a few seconds (and only penetrated, even by the Turks' accounting, by a little more than a mile), it's still possible that the GLONASS system used by the Russian military for navigation may have given the aircrew different information than the Turks had. GLONASS has fewer satellites than GPS, and more of its satellites follow the same orbital path. That makes positioning errors more likely. And with the complex border between Syria and Turkey (and Russia's operations against Syrian rebels taking them extremely close to that border), a slight miscalculation in flight path could put Russian pilots in Turkish airspace.

One crew member ejected safely; another, according to Russian officials, was killed by fire from Syrian Turkmen rebels on the ground as he parachuted down. NATO is holding an emergency meeting at Turkey's request. The Russian foreign minister has canceled a planned trip to meet with Turkish officials.

Further raising the stakes, a Russian Mi-8 helicopter searching for the two pilots was shot down by US-equipped Syrian rebels this morning, apparently using a US-made anti-tank missile. One Russian marine in the rescue crew was killed, and the helicopter made an emergency landing in "neutral territory," according to Russian General Staff spokesman Lt. Gen. Sergei Rudskoi.

Russian aircraft have repeatedly been accused of crossing into Turkish airspace recently during operations in Syria against rebels. Last month, Turkey shot down what was believed to be a Russian drone after it crossed the frontier.

But the Su-24 was in Turkish airspace for only seconds before it was shot down today, and diplomats at the NATO meeting told Reuters that they were concerned that the Turkish air force did not simply escort the aircraft out of its territory. There are some concerns that the Turks were simply waiting for the opportunity to shoot down a Russian jet—concerns magnified by the fact that a Turkish news crew was on site to capture the Russian jet being shot down.

As part of the safety procedures established by a Memorandum of Understanding between the US and Russia, both sides are supposed to communicate on a specific set of frequencies in the air and have a communication line open on the ground. The Turks were likely aware that the Russians were going to be operating close to the border, where they have been targeting groups supported by Turkey and the US—including the Sunni Turkmen militia that apparently killed at least one of the Russian pilots. Video, posted by militia members to Twitter, of the fighter going down was accompanied by cheers of "God is great!" as the plane crashed.

President Barack Obama today urged Turkey and Russia to de-escalate the crisis. But given the proximity within which Russian forces are operating to the Turkish border, and their attacks on people with political, religious, and even ethnic ties in common with the Turks, it is likely this won't be the last time that there's a conflict in the air near the border.