A method of operating a lifter for handling a rotor blade of a wind turbine, the lifter comprising at least one device (6, 8), for contacting an outer surface of the rotor blade, the lifter further comprises a non-optical wave based system for emission of a primary signal and for detection of a secondary signal, by the steps of: a) emitting a primary signal in a direction towards the rotor blade and detecting a secondary signal which is reflected at the rotor blade, b) analyzing the secondary signal to determine a position of the rotor blade with respect to the lifter, characterised in that further steps are: c) determining at least a section of an airfoil profile along a cross-section of the rotor blade, d) determining a plurality of theoretical airfoil profiles along various cross-sections of the rotor blade from a model of the rotor blade, e) matching at least the determined section of the airfoil profile with one of the plurality of the theoretical airfoil profiles to determine a longitudinal position of the lifter with respect to the rotor blade. wherein the lifter comprises at least one grabbing jaw (6, 8) having an antagonistic pair of arms (10, 12, 14, 16) which are moveable with respect to each other, wherein a direction of movement of at least one of the arms (10, 12, 14, 16) of the grabbing jaws (6, 8) defines a grabbing plane (E1, E2), and the method further comprises the steps of: f) determining a tilting angle (α1, α2) between the grabbing plane (E1, E2) and a longitudinal direction of the rotor blade, g) determining at least a section of a tilted airfoil profile of the rotor blade, h) determining a plurality of theoretical tilted airfoil profiles from the model, wherein the theoretical tilted airfoil profiles are tilted with respect to a longitudinal direction of the rotor blade by an angle which is substantially equal to the determined tilting angle, and i) matching at least the determined tilted airfoil profile with one of the plurality of theoretical tilted airfoil profiles to determine a longitudinal position of the lifter with respect to the rotor blade. a) emitting a primary signal in a direction towards the rotor blade and detecting a secondary signal which is reflected at the rotor blade, b) analyzing the secondary signal to determine a position of the rotor blade with respect to the lifter, characterised in that further steps are: c) determining at least a section of an airfoil profile along a cross-section of the rotor blade, d) determining a plurality of theoretical airfoil profiles along various cross-sections of the rotor blade from a model of the rotor blade, e) matching at least the determined section of the airfoil profile with one of the plurality of the theoretical airfoil profiles to determine a longitudinal position of the lifter with respect to the rotor blade. c) determining at least a section of an airfoil profile along a cross-section of the rotor blade, d) determining a plurality of theoretical airfoil profiles along various cross-sections of the rotor blade from a model of the rotor blade, e) matching at least the determined section of the airfoil profile with one of the plurality of the theoretical airfoil profiles to determine a longitudinal position of the lifter with respect to the rotor blade. f) determining a tilting angle (α1, α2) between the grabbing plane (E1, E2) and a longitudinal direction of the rotor blade, g) determining at least a section of a tilted airfoil profile of the rotor blade, h) determining a plurality of theoretical tilted airfoil profiles from the model, wherein the theoretical tilted airfoil profiles are tilted with respect to a longitudinal direction of the rotor blade by an angle which is substantially equal to the determined tilting angle, and i) matching at least the determined tilted airfoil profile with one of the plurality of theoretical tilted airfoil profiles to determine a longitudinal position of the lifter with respect to the rotor blade.