It has almost happened twice: a Russian military aircraft spying on a Western country turns off its transponder to avoid commercial radar and nearly collides with a passenger jet.
The most recent time was December 13 over Sweden. The time before that was March 3 over the Baltic Sea southeast of Copenhagen.
Both incidents are the result of Russia's probing Western defense capabilities in 2014 at a level not seen since the Cold War era. Russian planes have also flown up to and crossed Western states' borders and closely overflown Western naval ships to test NATO's response times and strategies.
"A lot of this is training in as close to a combat environment as you can get, particularly for the Russian Air Force," says Thomas Frear, a researcher at the European Leadership Network, a London-based think tank.
He says that over the course of 2014, NATO states have intercepted Russian aircraft probing alliance defenses more than 100 times. That is three times the number of intercepts in 2013.
The probes come as both NATO and Russia have heightened their military preparedness over the Ukraine military crisis and both sides seek to gather more intelligence about the other.
Russia has stepped up its military activities in the Baltic region while, at the same time, NATO has bolstered the capability of member states Poland, Lithuania, Latvia, and Estonia to resist any intimidation from Moscow.
The NATO initiatives include increased air patrols and reinforcement of naval task forces in the Baltic Sea region. Those, along with exercises in the Black Sea, constitute the largest mobilization of NATO forces on its eastern flank since the Central and Eastern European states entered the alliance.
Meanwhile, Russia has conducted major exercises for units in its Western and Southern Military Districts, including in areas bordering Ukraine. Western countries and NATO have called those exercises attempts to intimidate Kyiv at the same time that Moscow has sent soldiers and weapons to help pro-Russian separatists in eastern Ukraine.
The majority of the increased Russian probing of Western states' defenses has focused on the Baltic Sea region. But there have also been incidents along the U.S. and Canadian borders.
Those include Russian strategic bombers in international waters off Canada practicing cruise missile strikes on the United States in early September. And in May, Russian military aircraft approached to within 50 miles of the Californian coast, the closest approach since the Cold War.
'A Very Dangerous Game'
The more aggressive Russian probing carries a risk of dangerously escalating current tensions between the West and Moscow beyond the Ukraine crisis itself.
"The fact that it is being used in such a provocative way with a little bit of brinkmanship, getting close to borders or even crossing borders, that's of course a very dangerous game," says Marc Finaud, a senior adviser at the Geneva Center for Security Policy in Switzerland.
Frear notes that if a reconnaissance plane were to collide with a commercial flight as almost happened in December and March, NATO countries would be obliged by public opinion to pre-empt by force any future probes that could pose similar dangers. That, in turn, could lead to the downing of a Russian plane and create the conditions for a direct conflict.
Asked about the practice in his annual end-of-year news conference, Putin was defiant -- and placed the blame squarely on the United States.
"At the beginning of the 1990s, Russia fully abandoned the Soviet practice of sending our strategic air forces on patrol flights to remote regions. We stopped it altogether," Putin said.
"The American strategic flights with nuclear arms though kept going on. What for? Against whom? Whom have they been threatening? We kept refraining from flying year in and year out and we only renewed these flights two or three years ago. So who's the one provoking? Surely not us."
Adding to worries is the fact that the NATO-Russia Council -- the mechanism which NATO and Moscow created to deal with just such tensions -- has barely met since the Ukraine crisis began. Both sides have stopped cooperating to show their displeasure with the other.
That's a different pattern from crises during the Cold War, but not one that makes the world feel safer.
"The Cold War, for all its dangers, did have an element of predictability," Frear notes. "In a lot of respects, there was cooperation and a wider understanding of the rules of the game. [Those rules] just aren't in place now."
