Originally Posted by
kwflyer
After number 4, number 3 is the biggest. I've seen flex fares idbed due to late check in. The notion that idbed only applies to tango fares is foolish. If you can't check in online, Calling ac to notate that on your pnr will serve as your official check in time (which I've also seen) if it goes to an idb situation.
About 10 years ago, I nearly got IDB'd while holding a J ticket because of late check-in (T-24 minutes

). That was back when the check-in deadline for domestic flights were 30 minutes prior to departure. The check-in agent called the captain and asked if he wanted to let me on, which he did.
So there, seat assignment and check-in time are important to ensure you don't get IDB.