Apparently, for e-tickets, each coupon must be revalidated to match the actual live segment (flight/date/class) in the PNR in order for the check-in process to occur smoothly.

As far as I know, AA e-tickets actually do support OPEN segments! (Maybe only if issued in Sabre?) However, revalidation is not supported.

The following is from the AA travel agent website:

What happens is that when check-in for a flight opens, the airline's reservation system would send the Passenger Name List (PNL) for the flight in question to their Departure Control System (DCS). For most airlines, this process is transparent as the DCS and the reservations sytem is under one system (but divided between "reservations mode", and "DCS mode"), while at other airlines they can be totally seperate systems.

In some cities, an airline may even outsource their check-in functions to a local ground handling company or another airline (which may be using a different DCS).

(Sidebar: When you are doing online check-in at the airline's website, you are actually interacting with their DCS and not their reservations system. Also the reason why you can't check-in for some flights originating in certain cities for some airlines is most likely because they have outsourced their check-in functions in that city to another airline.)

Included in the PNL is a list of e-ticket numbers/coupons numbers associated with the passengers travelling on a particular flight. This automatically occurs if the flight number/date/booking class/city pair for the passenger matches the e-ticket exactly.

Sometimes when a change is made - yes this would include changing an OPEN segment to a regular segment (in reservations mode), the flight segment becomes disassociated with the e-ticket coupon in the PNR. If this occurs, when check-in opens and the PNL is sent to the DCS, there would be no e-ticket number/coupon associated with the passenger on the PNL for the flight in question. When the passenger attempts to do online check-in, they would get an error message telling them that OLCI is unavailable. Also, if the passenger arrives at the airport check-in counter, they would be told that there is no e-ticket associated with their booking and directed to the ticketing desk (as most check-in agents only have access to "DCS mode", while the ticketing desk may have access to both "DCS mode", and "reservations mode").

To avoid this from happening, when a change is made, the e-ticket coupon (which may originally be an OPEN segment) must be revalidated to match the details of the new flight. For some airlines, this automatically occurs when the cancel and rebook of the segment occurs in the same transaction. At some other airlines, the agent must use the revalidation function to revalidate the e-ticket coupon. While at other airlines (i.e. AA), an exchange and reissue of the entire e-ticket needs to be done as revalidation is not supported. Note: This is done in "reservations mode".

If revalidation is not possible (for an AA e-ticket), another option would be to link the new sector to the e-ticket coupon with the OPEN sector using a SSR TKNE message.

If you ask CX to do this, they will charge you a service fee of HKD 300.

Once these steps are done, then the passenger can check-in normally.

When a passenger is checked-in/boarded, the DCS updates the e-ticket coupon with "CKIN"/"FLOWN" status in the validating carrier's e-ticket database. (In most cases, this is done interactively [if the DCS resides on the same host as the airline], whlie in other cases this is done in batches [if an outside ground handling agency is used]).

(Sidebar: There may be cancellations / new reservations for a flight after a flight has opened for check-in. What happens is that the airline's reservation system would periodically send an "Additions and Deletions List" (ADL) to the DCS.)

Hope this helps!