And the AIP Australia says...
7.1.9 A pilot operating a Mode S transponder must:
a. Not relevant.
b. On receipt of ATC clearance, or requesting the earlier of Push Back or Taxi, select TA/RA/XPDR/ON AUTO as applicable.
Note 1: If AUTO mode is not available Select ON (e.g. XPDR) and assigned Mode A code.
Note 2: Australia does not require TA/RA to be de--selected while aircraft is on ground.
c. When parked and shutting down engines, select STANDBY.
d. Not relevant.
7.1.10 Pilots must select the transponder to STANDBY before effecting an SSR code change and returning the transponder to ON/ALT.
Note: This action is required to prevent possible loss of displayed aircraft position/label information and possible misidentification of aircraft in automated Australian ATC systems due to temporary selection (while effecting the change) of a code already in use.
