It was found that a newly developed portable collision alert radar receives reflections from the ground while flying. In this paper a method is developed that uses range and Doppler information from these reflections. This information is used to compute height and velocity information relative to the terrain, something which is not possible with existing hardware. The method was tested on a local flight in the Netherlands, with a prototype of the radar. Flight state results were compared with those of a GPS tracker on board. It was found that the velocity can be computed within meters-per-second accuracy. Height differences are due to the measurement method, measuring directly from the ground surface (radar) or relative to a database (GPS). If developments in microwave sensing techniques continue to improve the hardware, flight state estimation by radar can become an option for pilots who do not want to be dependent on the correctness of a terrain model, but who measure the terrain shape independently.