It would be interesting to see an example how an ultra long haul such as Dubai to LAX is planned and where the enroute alternate would be. The logistics of lobbing in to say Vancouver and how to continue the flight must be interesting.
The Lufthansa 747 that ended up at some little known Russian airfield this week en route from China demonstrates some of the issues. The pax apparently sat on the plane while the crew took their mandated rest. At least there is a terrific hotel at Vancouver airport!