Originally Posted by TerryK
It is possible as long as both fares allow combinations. You need to look into the fare rules, not just booking codes, of each fare to see if it is possible.
Exactly. Actually, a number of web sites automatically do this for you if the fare basis allows it (e.g., outbound in U, return in H) if you are looking for the lowest fare. If you want a QUP fare going one way and a less expensive ticket on the return, however, the booking can be a bit tricky.