Originally Posted by bwc175

I don't have any info on how the app indicator actually works, but they know what flights people are on when they enter a club. It shouldn't be difficult to subtract people from the in-club census based on flight boarding times. There could be some inaccuracy due to delays or flight changes if live flight status data isn't used, or if people leave the club early. It would take work, but for another step up in accuracy, the data exists in their systems to track "boarded" status of each person who entered, so there could be certainty that boarded passengers are no longer in the club, even if there is some delay between when they actually leave the club and board their flights.