Originally Posted by
mattjp
The rules sheet says that: "Where the applicable booking class for the lower class is not available ... Passengers travelling on DONE* Business Class Fares may book B class (except AA) or H class on AA".
There are a number of booking classes allowed to be used on a D or A xONEx depending on where the flight is or why D/A is not available.
eg, domestic Japan flights book into F/J/Y.
single class AA flights on First or Business RTWs book into Y.