Sorry I'm fairly new in air travels... what is a MCO? It sounds like a airline issued credit note from reading the posts above. When is it ususally issued? My past experience from changing a reservation is to submit my ticket to the travel agent for an exchange for a new ticket plus the penalty fee. For refundable tickets, you get the money back... So when is MCO needed usually?

Sorry that I ask this silly question... but after reading 10 posts regarding "MCO", I am really curious to what it stands for.