Thank you Concerto, timol and sjharte (Stephen) for introducing the “interlining rule” (= combination possibilities of several airline within one award ticket or upgrade) to the board.

Concerto is right, interlining between LX/CX is not permitted. For example the routing ZRH-HKG-SIN-HKG-ZRH could be issued completely on CX (= one award ticket), assuming that LX´s ZRH-HKG-ZRH still has a CX code share number.

sjharte (Stephen) is right, that you can't have AY and TK on the same award ticket. Interlining with AY is permitted with FU/IW/LO/LX/PE/SN/TP/VA only.