In this paper we examine the potentialities of an innovative surveillance system composed by passive and active radar sensors for enhancing the security level in small airports and private runways. Specifically we report on the R&D activities carried on within the EU project SOS (Sensors system for detection and tracking Of dangerous materials in order to increase the airport Security in the indoor landside area). These activities included a number of experimental campaigns where both the single sensors and the multi-sensor system have been extensively tested. To this purpose, we employed the WiFi-based Passive Coherent Location (PCL) receiver developed at SAPIENZA University of Rome and a Ku-band frequency modulated continuous wave (FMCW) radar developed by MetaSensing. Both the considered sensors allow a radar coverage suitable for the extent of a small airport area, though providing target measurements with very different accuracies. The experimental results reported in this paper prove the effective applicability of the proposed approach for small airports surveillance.