It is indeed interesting to note that even without any autopilot in use the AT goes into RETARD mode at "approximately" 27ft RA. Our SOP is to not switch the AT completely off when flying manual approaches but rather to de-select SPEED and have a low-speed protection available. If that is the case you will get a RETARD around 27ft even if you have the thrustlevers allready at idle or if you are in the process of retarding them.