The subject of the invention is a door drive for a swing door of a passenger transport vehicle, comprising a rotary post, which is arranged at the vehicle, with at least one pivot arm for arrangement at a door leaf, wherein a motor is arranged in the rotary post and is connected with the rotary post, wherein at least one planetary transmission stage is provided for stepping down the rotational speed of the motor and wherein the pinion cage of the at least one planetary transmission stage comprises a rotary element, particularly a pinion, which is fixable.