The US Department of Transportation (DOT) Volpe Center is currently involved in a National Aeronautics and Space Administration (NASA) project to configure, deploy, and evaluate the capabilities of a transponder multilateration and automatic dependent surveillance-broadcast (ADS-B) system that will perform aircraft tracking in the Gulf of Mexico offshore area. The helicopter in-flight tracking system (HITS) is being assessed for use in an offshore area where several hundred petroleum industry helicopter flights occur daily, and where there is currently little secondary surveillance radar coverage. Although multilateration has been extensively tested for airport surface applications, there is limited experience in the tracking of airborne aircraft. The HITS project provides an opportunity to evaluate multilateration and ADS-B technologies as potential alternatives to established secondary surveillance radar (SSR) as air traffic control surveillance systems. This paper describes (1) the derivation of multilateration and ADS-B system requirements, in order for these systems to provide equivalent capability to the Air Traffic Control Beacon Interrogator Model 6 (ATCBI-6) SSR system now being installed in the National Airspace System; and (2) procedures being implemented to test the HITS multilateration/ADS-B systems against the requirements.