Originally Posted by Nikko5

You will be forced landside on arrival, even for domestic (out past baggage claim & through customs). So not like Jersey, where you can loiter airside and go straight back to the gate (or any other gate).

After customs in GCI, it’s then a very short walk (20 yards?) to re-enter security, which is normally relatively quite (outside e.g. the early morning bank of departures).

So if you had your return boarding pass & sitting fairly near the front on outbound, I suspect it would be fine, probably back to the gate before the passengers down the back had finished disembarking.

Unfortunately I have no idea on Fly (and whether BA do now use it at GCI). I know there were problematic airports in the past not using Fly which meant airport check-in only for the return and even e.g. Heathrow could not pre-print your return boarding pass.