Originally Posted by exAC
Even more complex than that.
These are enroute alternates. If SEA, PDX, SFO are all forecasted to be fogged in then the flight could need to hold enough fuel to divert to LAX or even further inland like LAS. There would need to be enough fuel onboard to divert to these places up to half way across to HNL.
It is much more rare not to e able to plan a suitable airport somewhere in the islands.
Yes, and they are contingency airports.
For example, in the event of an enroute engine failure or pressurization loss, you must have someplace to go if you want to fly more than 60 minutes from a suitable alternate (ETOPS). Fuel for this is considered in the worst case scenario, speed, wind, engine anti-ice are all factors that are applied here.