toz100

I tried to change my return flight date online via 'manage my booking'. It doesn't work and I get a notification that on this flight there are no seats available. I tried this for multiple dates and with the 'my dates are flexible' box activated. I should add that the booking consists of 2 legs outbound and inbound resp. and has mixed cabin classes. Moreover the outbound flight(s) is(are) still in the future.

Any ideas what could be the reason for the problem? Is it maybe the mixed cabin classes? Do I have to call SQ?

demue

You need to give more info. Route, class of travel, fare paid (revenue / KF saver / advantage redemption), already flown a portion of the ticket, etc. No one can guess what your specific situation is.

If this is a redemption ticket and if you are not QPP (PPS) or TPP / LPP (Solitaire), IIRC you cannot change the return portion (date, flight number, etc.) of the ticket any longer once the first outbound segment has been flown, you are locked in unless the airline makes operational changes which may give you the opportunity to move things around, but those are special circumstances.

If it is a revenue ticket ($$$) then it depends on the specific fare and the associated rules and it gets even trickier. If revenue fare, you better call SQ and ask whether changes are permitted and at what cost. Also be aware for paid fares where your outbound may be fare type AAA and return fare type BBB the fare conditions of the lower, more restrictive fare apply to all flights. E.g. you have Business D fare outbound and Business J fare inbound, even though you want to change the flights booked under the quite flexible J fare portion, the fare rules of the D fare reign "supreme" in this case. YMMV.

toz100

It is a revenue ticket. The routing is JFK-SIN-SGN rt. and as mentioned before the outbound flight has yet to come. The long legs are in PE lite snd the short legs in economy. The T&C's I got with the booking say that the PE legs can be changed for a fee of 100 USD plus any fare differences. Interestingly there is no information about the economy legs.

demue

Ok, I missed the "future" part. So a PE Lite fare should be changeable against fee. Just need to make sure your entire RT is booked under the same fare (assume it's R fare) and not a mix of R and possibly some Eco Lite (K, V) which don't allow changes, but that would be weird and unlikely you could have booked it that way.

Best to call in this case, as you said, could be online engine struggling with the PE / Eco cabin mix even if all booked under R fare. Availability could be the other reason or some married segments, but try reservations first before we speculate too much.