International diversions

AAL7 from DFW to BNE was diverted to Fiji today, with plans to continue onwards tomorrow and I have so many questions!

1. The flight crew handed out entry forms prior to landing - do they just carry these around just in case? For all countries?

2. Passengers were told that they are required to take the next leg of the flight tomorrow - what happens if they just don’t? There are other flights to Brisbane before then, are they allowed to book and take one of those instead?

3. AA is claiming the diversion is due to stronger than forecasted headwinds - does this mean someone miscalculated or can headwinds actually vary that much and make that much of a difference? Does it mean they were close to MTOW and probably couldn’t have loaded more fuel?

Flight operations are so fascinating! Thank you!