Beginning a third week holed up in a Moscow airport's transit zone, Edward Snowden finds himself far enough away to evade U.S. 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 traveling over or refueling in a U.S.-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. Snowden faces felony charges in the United States for leaking classified documents that detailed the National Security Agency's extensive surveillance apparatus.