Originally Posted by
ecgz88
1. For cash purchased Y try upgrade in airport to J, is there any requirement for which Y class I should buy?
2. Except departure from UK, when I upgrade in airport I just need pay the miles difference? or I still need pay tax/fees difference?
1. "Special' fare tickets are not upgradable at all. Saver can only be upgraded at the airport or on board. Flex and Flex+ can be upgraded at any time (subject to availability of course). The lower the fare class, the more miles it will cost to upgrade. Details are in the mileage calculator on the website (it's under 'Loyalty')
2. In my experience you just pay the miles. The UK is an exception as you already mention (because of the APD, although this is not collected for an 'on board' upgrade). I am not aware of any other exceptions but I cannot categorically state that there are none.