In close collaboration with our industry partner Skyguide we successfully developed and tested a mobile system for accurately tracking arbitrary civilian aircraft. In this project we apply the principle of multilateration to compute the aircraft position. Several field tests conducted around Zurich airport demonstrated that the system allows to track the aircraft with a horizontal accuracy of roughly 8m. The system is designed in such way that it can be transported, assembled and operated by a single person. As it does not rely on radar and is equipped with an autonomous power supply, our system also lends itself very well for operations in remote areas.