Retractable step having a lifting and ramp function

A boarding system for a passenger transport vehicle, the boarding system comprising:

• a retractable step having a lifting and ramp function, wherein an extendable front edge of the retractable step and a rear edge of the retractable step which is arranged in the rear in the direction of travel, are adjustable in terms of height,
• an extending drive for retracting and extending the retractable step, wherein the extending drive has an extending motor and a lifting gear, wherein the lifting gear translates an extending movement of the extending motor into an at least partial pivoting movement of the retractable step, so that the pivoting movement of the retractable step causes a change of height of the front edge and/or of the rear edge, and
• an extending unit, with which the retractable step is movably coupled via the lifting gear,
• wherein the lifting gear has a first lifting element and a second lifting element, which has a substantially elongated shape, wherein the first lifting element and the second lifting element is in each case connected in an articulated manner to the extending unit and to the retractable step and arranged at a distance from one another, wherein the first lifting element is pivotably coupled to the retractable step in an area between the front edge and the rear edge by means of a first joint to the retractable step and is pivotably coupled to the extending unit by means of a second joint, and that the second lifting element is pivotably coupled to the retractable step in an area of the rear edge by means of a third joint and is pivotably coupled to the extending unit by means of a fourth joint, wherein the fourth joint additionally has a translational degree of freedom in horizontal direction, wherein the fourth joint is coupled to the extending motor.