30-year-old American Edward Snowden, a contract employee at the National Security Agency, is the whistleblower behind significant revelations that surfaced in June 2013 about the US government's top secret, extensive domestic surveillance programmes. Snowden flew to Hong Kong from Hawaii in May 2013, and supplied confidential US government documents to media outlets including the Guardian.
Edward Snowden's flight path to asylum fraught with risk
Plotting a great escape that doesn't cross airspace of US-friendly nations would be difficult
Beginning a third week holed up in a Moscow airport's transit zone, Edward Snowden finds himself far enough away to evade US authorities, but also too far from any of the sympathetic nations willing to shelter him.
Aviation experts say that even if Snowden accepts the tentative offers of Venezuela, Nicaragua or Bolivia to give him shelter, it's virtually impossible to chart a flight plan to those nations that doesn't include travelling over or refueling in a US-friendly country that could demand inspection of the plane - and detain him.
Nations have full, exclusive jurisdiction over their airspace, so any plane carrying Snowden could be forced to land if it flies over the territory of a country that's willing to help American authorities capture the fugitive intelligence contractor.
"Nations control their airspace up to the heavens," said John Mulligan, an aviation law expert at DePaul University's College of Law. "Just look at the map. It's probably possible to figure out a route that wouldn't touch the airspace of the United States or any friendly nations, but it wouldn't be easy."
Snowden's best hope for breaking out of the transit area most likely hinges on whether he could sneak onto one of five weekly, direct flights to Havana. The main drawback? The path takes the plane directly over the US, which could flout a standing treaty and force a scheduled commercial flight to land.
There are planes that can make the 9,600 kilometre direct flight from Moscow to Havana or Caracas with fuel to spare. The Airbus A340 has a range of about 14,400 kilometres and a Boeing 777 can fly about 600 kilometres further before refuelling.
But a direct flight would mean passing through the airspace of European nations and possibly the US. And chartering such a craft would be incredibly expensive - US$100,000 to start, and that is if a charter service could be found willing to risk angering Washington and perhaps being accused of aiding a fugitive.
"I don't know what sort of plane they'd have available to make that flight, especially without refueling," Mulligan said. "A refueling stop would probably be problematic for Snowden."
While US President Barack Obama has said he would not be "scrambling jets" to haul in Snowden, the US government has shown that it can pressure countries that would serve as pit stops for Snowden on his way to Latin America or other potential exile destinations.
Snowden has petitioned more than 25 countries for asylum; the State Department has promised "grave difficulties" for bilateral relations with any nation that aids his escape.
Last week's diversion of Bolivian President Evo Morales' presidential jet as he attempted to return to Bolivia from Moscow was a cautionary tale for Snowden as he mulls exit strategies from transit-lounge limbo. France, Spain, Italy and Portugal denied Morales' requests to overfly their airspace on the way to a refuelling stop in the Canary Islands.
The president's plane was rerouted to Austria and spent 14 hours there, touching off a diplomatic firestorm that may have made some Latin American nations even more willing to play host to Snowden, but also showed the limitations of their ability to help him.
"I would think it's very instructive and worrisome for Snowden," said a US aviation expert, speaking on condition of anonymity. "Those states were on absolutely firm legal ground to deny [Morales] use of their airspace. Politically? That's a judgment call."
"He's in a pickle," the aviation expert said, adding that he could not recall a similar case in his long career in the industry. "He'd want to be sure that every country he's flying over or refuelling in wouldn't arrest him."
And lurking under all the problems with air travel is another logistical kink: Snowden's lack of travel documents. His US passport was revoked, so it is unclear how he would be processed out of Moscow.
In other asylum cases - those not involving fugitives accused of revealing state secrets - refugees have travelled on specially issued United Nations passports, or other temporary country-issued documents.