I am trying to book a simple MEL-HKG-MEL itinerary with one small hitch: I want to travel premium eco flex on the outbound and eco flex on the return (travelling with family on the way back only).

You can book this online, because when you search for eco fares, it shows you premium eco as well. But when I do this, it shows me that my preferred outbound flight is sold out in premium eco. However, if I start a search for premium economy fares, it has premium economy (W class) still available for that same outbound flight. Of course, that's no good because then it doesn't give you the option to book a lower class for the return.

Calling the service centre brought the same response, no premium economy left on my preferred outbound flight.

The only explanation I can think of is that you can't combine W class premium economy with K class economy? But this doesn't make any sense - I'd be happy to pay more to get on my preferred outbound flight, why wouldn't Cathay just take my money?

Ex-HKG, I can book this kind of ticket. When I search Economy, it gives me the option for Y+. Then for the inbound, it still allows me to choose Y.

Maybe it's something to do with the fare rules for Australia point of sale.

Yes, my understanding is K can't combine with W... K can only combine with R...

If you need to combine econ with W, it can only be Y... And what's "wonderful " about CX's online system is you are nearly impossible to book Y directly online now...

Problem solved: It appears that while you cannot book W and K classes together, you can book R and K classes and then change flights, in the process upgrading from R to W for the fare difference. So the end result is what I wanted, W on the outbound and K on the inbound.

Interesting operation... Previously they won't let me do so... Thanks for sharing