Surveillance information forms the basis for providing traffic separation services by Air Traffic Control. The consequences of failures in the integrity and availability of surveillance data have been highlighted in near misses and more tragically, by midair collisions. Recognizing the importance and criticality of surveillance information, the U.S. Federal Aviation Administration (FAA) in common with most other Civil Aviation Authorities (CAAs) worldwide has implemented a surveillance architecture that emphasizes the independence of surveillance sources and the availability of crosschecks on all flight critical data. Automatic Dependent Surveillance Broadcast (ADS-B) changes this approach by combining the navigation and surveillance information into a single system element. ADS-B is a system within which individual aircraft distribute position estimates from onboard navigation equipment via a common communications channel. Any ADS-B receiver may then assemble a complete surveillance picture of nearby aircraft by listening to the common channel and combining the received surveillance reports with an onboard estimate of ownership position. This approach makes use of the increasing sophistication and affordability of navigation equipment (e.g. GPS-based avionics) to improve the accuracy and update rate of surveillance information. However, collapsing the surveillance and navigation systems into a common element increases the vulnerability of the system to erroneous information, both due to intentional and unintentional causes.