It is well known that by means of airborne interferometric SAR systems it is possible to generate high precision Digital Elevation Models (DEM), although these platforms are seriously affected by motion instabilities. These deviations are recorded by navigation systems, such as GPS receivers and inertial units. The precision of these systems, and the subsequent off-line processing, determines the level of confidence in the generated heights. Errors in track knowledge lead to incorrect generation of the interferometric phase, which yields height errors in the final DEM. In this paper it is shown an analytical work which is useful to analyze the consequences of such factors onto the bias and the standard deviation of the height errors in Digital Elevation Models.