The Federal Aviation Administration's (FAA) Next Generation upgrade proposes a fundamental transformation to thenational airspace system (NAS) that aims to reduce dependence on outdated radar infrastructure, increase airline safetyand condense required aircraft spatial separation. A key component of the upgrade is the Automatic DependentSurveillance-Broadcast (ADS-B) system. ADS-B provides continual broadcast of aircraft position, identity, velocityand other information over unencrypted data links to generate a precise air picture for air traffic management. Officialdocuments claim operational requirements necessitate unencrypted data links while maintaining that there is a lowlikelihood for malicious exploitation. This paper studies the security vulnerabilities associated with the ADS-Bimplementation plan and develops a taxonomy to classify attacks and examine potential impacts the attacks have onoverall NAS operations. The taxonomy helps provide a comprehensive understanding of the threats associated withADS-B implementation and facilitates risk analysis and risk management.