In addition to FCS explorer and a minor correction. A system the gear and B system the flaps. The standby can be activated manually or automatically to power thrust reversers rudder and leading edge flaps/slats (extend only). Automatic operation of the standby is initated with loss of system A or B or rudder pressure reducer system fails in low pressure mode(classic),and flaps extended. In aus we always push back with a nose gear steering lockout pin installed however if that wasnt available we would depressurize system A.