Aspects of the present invention relate to a nacelle (14) for a wind turbine generator (10), and a method for transferring components into and out of a wind turbine generator (10). The nacelle (14) comprises a housing (26) surrounding an internal volume (24) of the nacelle (14). The housing (26) has a maintenance opening (50). The nacelle comprises a carriage (54) configured to hold a component (48), the carriage (54) being movable between a first position and a second position to transfer the component (48) through the maintenance opening (50). When the carriage (54) is in the first position, the component (48) is held within the internal volume (24). When the carriage (54) is in the second position, the component (48) is held such that at least a portion of the component (48) is outside the housing (26).