The diversion airports are chosen specifically for each stage of the flight, so a flight doesn't ever need to return to where it came from.

Oceanic flights are planned so that at every point along the route, the aircraft can lose an engine or cabin pressure and still reach a pre-approved diversion airport with enough fuel, with the flight plan marking the points where turning back versus continuing becomes the faster option. If a diversion is needed mid-ocean, the crew offsets from their assigned track and altitude to stay clear of other traffic, then heads to the nearest suitable airport, such as Gander, Keflavik or Shannon over the Atlantic, or Anchorage, Cold Bay or Midway over the Pacific.

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12_throw_away 4 hours ago | parent | next [-]

I'm not aware of a requirement that you need to always be able to divert to a different country.

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lxgr 4 hours ago | parent | prev [-]

Please suggest an appropriate international alternate for a plane just about to land in Denver with an hour of fuel remaining.

Alternate airports are picked based with regards to all kinds of contingencies (many of them meteorological), but "the US closes literally every airport" is not one of them.

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aschla 4 hours ago | parent [-]

That likely falls within the case-by-case basis the FAA mentioned, and would likely be allowed to land at a U.S. airport that has capacity.

	▲	filleduchaos 16 minutes ago \| parent [-]
		And that's exactly why you got the reply that international flights MIGHT not have enough fuel left to divert (and thus obviously have to be allowed to land within the continental US), but for some reason you insisted that every flight would be able to.