Performance Margins of Secondary Surveillance Radar Transponders

A secondary surveillance radar (SSR) transponder, operating within the 1030/1090 MHz frequency bands, is a critical component of cooperative surveillance systems, including aircraft collision avoidance systems. As a single point of failure, a malfunctioning transponder renders cooperative detection inoperative, risking the loss of an aircraft's track even within highly redundant surveillance networks. While such failures have occurred in the past, their root causes and likelihood of recurrence remain inadequately understood, necessitating a proactive approach. This article introduces a methodology for evaluating the real performance limits of SSR transponders, focusing on overinterrogation events recorded in Europe that could lead to transponder denial of service. It applies this methodology to assess the performance of various transponder types and provides recommendations for effective monitoring and early warning systems to mitigate the risks of transponder overinterrogation.