In what case airline companies upgrade from economy to business class w/o extra fees?

Airlines use upgrades to take care of their most profitable customers. If you are a high-mileage frequent flier or bought a full-fare ticket, you may be able to get an upgrade.





If you're an occasional traveler on a nonrefundable ticket, then forget about it. Those types of tickets usually lose money for airlines and they are not going to use valuable upgrades on them.In what case airline companies upgrade from economy to business class w/o extra fees?
an example...my boyfriend flew home to Trinidad from New Jersey over Christmas. The flight was overbooked and they ticket agents asked him if he were willing to give up his seat and take a later flight. He aggreed and because he was understanding, they bumped him up to first class. He got to wait in the first class waiting lounge and everything.





I think it's extremely rare that you get it for free nowadays but it has to be some circumstance that the airline couldn't forsee and you're understanding about it. You can't just ask for it, for free. In what case airline companies upgrade from economy to business class w/o extra fees?
you can upgrade your ticket with paying amount of business class and if seat is available