C. Bloggs: Generic RVSM requirement to have XPDR coupled to whichever altimeter is feeding the active AP.
By 2005 the factory Airbus SOP did not have the requirement to set XPDR 1 vs. 2 according to PM/PF (on-side autopilot to be used accordingly). They favoured ATC1 always, electrical emerg conf being the reason I was given.
Later, around 2008, the following note was added:
Originally Posted by FCOM PRO-NOR-SOP-06: PEDESTAL -> ATC
For RVSM operations (Refer to PRO-SPO-50 General), select SYS 1 if AP 1 is used, and SYS 2 if AP 2 is used.