See message 2 in http://flyertalk.com/forum/showthread.php?t=678150 for an example.

A friend told me another example; he arrived a little bit after the listed checkin time, and they would not let him check in, although he would have made it on the plane before the door closed if they did let him check in. However, not long afterward, I was on a flight on the same airline, the last passenger to board appeared to have just run through the terminal, telling her friend that it took only 10 minutes to get to the plane from her late arrival at the airport (flight was almost, but not quite, full).

Seems that the airline in question was lenient with checkin time in the case of a non-full flight, but strict in other cases. Could it be that the other cases involved overbooked flights, and the airline wanted a way of getting passengers off the flights without having to offer VDB or IDB compensation, or list an IDB on their record?

Could she have checked in online and then been able to run through the terminal? From what I have seen, the airlines are pretty strict on their check-in requirements across the board. YMMV of course.

I don't think it's a big conspiracy like you think it is. Checking in is not the same thing as boarding the plane. The 2nd person seemed to have come in from another flight, presumably from the same airline. If that's the case, she probably checked in before her first flight for all of her flights that day - well before the listed checkin time. Therefore, she checked in before the checkin time, and your friend checked in after the checkin time - hence the discrepancy in policy.

they do try and use late check-in to deny IDB. One case I recall was a guy with hsi family who checked in on-time but the airline claimed he was outside of the cut-off and denied him boarding (the flight was oversold as well). For some reason he had proof that he checked in in time (I think he asked for a print-out at the check-in desk of his PNR which proved to be time stamped) and he won a case against the airline in small claims court.

They enforce it on connections, too. I had a miserable late departure on AA from HPN in a jungle jet where they took forever to re-distribute pax so the weight would be even- took off an hour late. Of course we arrived at the end of one terminal in ORD and my connection was at the end of the next one. I had carry-on only and ran through the corridors, arriving 5 minutes before scheduled pushback. No dice. Door closed. Game over. I'm sure they were able to put a standby in my seat, so they left without me.

Ryan Air seems to take it even one step further. They will not check you in if you arrive even 30 seconds after the deadline (and it doesn't matter if you are late because you have spent 1 hour waiting in their line).

They will, however, offer to sell you a new ticket for the same flight at the walk-up fare which will be fine even for "late" check-in.

HTB.

I wonder if planes would ever leave on time if they didn't enforce these rules?