A tower crane comprising a tower on which a rotating portion is pivotally mounted along an orientation axis by means of a pivot mechanism, said pivot mechanism including at least a motorized orientation system, a mechanical orientation brake and an angular detector capable of detecting an orientation angle of the rotating portion, said tower crane being configurable between a service configuration in which the rotating portion is rotatably driven on the tower along the orientation axis by means of the motorized orientation system, and an out of service configuration in which the rotating portion is rotatably released on the tower according to the orientation axis in order to be able to be oriented in the direction of the wind, said mechanical orientation brake being deactivated in the out of service configuration, said tower crane comprising a control/command unit connected to the motorized orientation system, to the mechanical orientation brake and the angular detector, said tower crane being characterized in that, in the out of service configuration, the control/command unit activates a monitoring mode in which the control/command unit detects, as a function of variations in the angle of orientation of the rotating portion or as a function of variations of an angular speed of the rotating portion established from the variations of the orientation angle, if the rotating portion is in one of the following instability states: - an autorotation state, corresponding to a rotary movement of the rotating portion in a given direction over at least one complete turn, characterized by a variation of the orientation angle according to an angular amplitude at least greater than one angular autorotation threshold of at least 360 degrees in a first given time interval or at an angular speed greater than a given autorotation speed threshold; or - an oscillation state, corresponding to a back and forth movement of the rotating portion about the orientation axis, characterized by at least one cycle of variations of the angle of orientation in a first direction then in a second direction, opposite to the first direction, characterized by an angular displacement of the orientation angle at least equal to an angular oscillation threshold comprised between 20 and 180 degrees in a given second time interval or at an angular speed greater than a given oscillation speed threshold. - an autorotation state, corresponding to a rotary movement of the rotating portion in a given direction over at least one complete turn, characterized by a variation of the orientation angle according to an angular amplitude at least greater than one angular autorotation threshold of at least 360 degrees in a first given time interval or at an angular speed greater than a given autorotation speed threshold; or - an oscillation state, corresponding to a back and forth movement of the rotating portion about the orientation axis, characterized by at least one cycle of variations of the angle of orientation in a first direction then in a second direction, opposite to the first direction, characterized by an angular displacement of the orientation angle at least equal to an angular oscillation threshold comprised between 20 and 180 degrees in a given second time interval or at an angular speed greater than a given oscillation speed threshold.