Statistics generally (there are exceptions of course) makes very broad assumptions about independence and random selection of your samples.

For a group of people as correlated as having the same destination at exactly the same time using the same airplane I would be very wary of applying any statistics at all, even ignoring the possibility of a large group.

Hundreds of otherwise independent people can decide to not show up simultaneously due to terrorist attacks, corona, a cheaper alternative, a conference being cancelled, etc.