It's psuedo-random based on when you get your boarding pass (starting 24 hours)....

		sjg007 on Jan 16, 2020 \| parent \| context \| favorite \| on: Letting slower passengers board airplane first is ... It's psuedo-random based on when you get your boarding pass (starting 24 hours). Essentially the quest for a non-middle seat conditional on distance to the front door.