Originally Posted by
jcfr22
... But the other flights are operated either by Air China and Lufthansa. United.com says advanced seat assignments are not available for those. .....
Seat assignments are done by the flight operator, not by UA.
http://www.flyertalk.com/forum/unite...-alliance.html
It can help to have the operating airlines PNR for your flight when you contract the operating airline, see the wiki graphic to find those.
In some cases partner airlines are not assignment seats in advance or for free, but that should not be an issue in these cases.