Automatic Dependent Surveillance ? Broadcast (ADS-B) is an emerging Communications, Navigation, and Surveillance (CNS) technology that will vastly expand the state of the art in CNS in the National Airspace System (NAS). However, ADS-B is not currently secure and foolproof, and is currently vulnerable to abnormalities and deliberate contamination (spoofing). To address these problems, Metron Aviation, Inc. designs and develops an innovative software system that Verifies and Validates (V&V) the integrity of an ADS-B signal in real-time, independent of a secondary truth source of surveillance data. The system uses a suite of Kalman filters for short time horizon trajectory predictions, bearing signal tracking, a novel intent inference algorithm for reasoning about ADS-B intent data, and confidence assessment measures. The proposed technology addresses NASA's quest for technologies to harden aircraft CNS systems against abnormality and deliberate attack.