Originally Posted by PV_Premier

whatever it was, it was deemed safe to fly to SFO and it is easier for them to do MX and swap frames at SFO than anywhere else along the way (save, perhaps NRT). one reason they may not have continued to NRT is that whatever the issue was resulted in insufficient ETOPS clearance...?

putting a crippled 772 down in ANC or SEA would require the relief crew to fly to ANC or SEA then on to HKG, perhaps putting them at risk of timing out by the time they got boarded up and out of ANC.

so everyone was forced to spend that much more time on the UA plane to get to SFO, but this probably gave them the best shot of getting the pax to HKG in a "timely" manner with minimal additional disruption.

just an outsider perspective...no inside info whatsoever.