Check-in: What is “Online Check-in”?
Most airlines offer you the possibility to pre-arrange check-in and seating online from their websites. This can normally be done from between 22 hours or 3 days before a departure so you should check the relevant airline(s) when they open up for online check-in.
We recommend you use the airline's facilities to check-in online when available. Unless you want to wait to do it until you are at the airport, but then you should expect that the only seats left probably will be the ones in the back next to the toilets. You also risk not to be seated with your travel companion(s) if you wait to arrange the seating until the airport.
Note that the 'operating airline' might be different than the 'marketing airline' in which case you should go to the 'operating airline' for online check-in. You should also note that the 'reference' sometimes required by the airline is not your 'KILROY reference' but the airline reference you find in your online itinerary at www.tripcase.com