Many airlines and airports now have conformance checks. Take BA and T5 for example. You must have your boarding pass scanned at least 35 mins before departure. If you arrive after this cut off, you will be refused to go through security. Most, if not all European airports now have boarding pass scanners at security. When the load control department tried to update the zero fuel weight, pax number and baggage reconciliation for the flight, those who have checked in online, but not passed through security are noted. Therefore if no bags were checked in, and the passenger has not been logged as passing through security, the passenger is automatically offloaded at gate closure ( usually 15 mins before STD). Should bags have been checked in, obviously the individual is somewhere in the facility. In this case the bag is usually held aside at the aircraft before being loaded. This does not always happen, and hence delayed due to no-shows with checked in baggage that has been loaded.
Should a flight be overbooked, at a pre determined number, online checking stops processing, claiming an error etc, forcing passengers to checking at the desks. At this point frequent flyer, fare class and sequence number rules come into play along with asking for volunteers to be offloaded.
Last edited by BUGS/BEARINGS/BOXES; 21st May 2012 at 19:17.