In an obstacle device, a front end range imaging sensor is used to scan the viewing field relative to the aircraft, while a navigation system provides information concerning the postion and altitude of the aircraft. A data processor uses these data to generate 3-d scene vectors, such that every range image is converted into a measurement point set, from which the presence of cables or wires is detected using a wire detection procedure based on the Hough Transform. For this purpose, an HT acceleration board is provided, which needs not perform complex floating point operations. The processed results are then input to an evaluation module, which determines whether any detected wires are proximate to the position of the aircraft.