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The system of air-ground communications is one of the most fundamental elements of air traffic control in the National Airspace System (NAS). The current air-ground voice communications systems are using the more than 50-year-old analog voice transmission technology in the licensed air traffic management VHF spectrum band. The limited spectrum is allocated statically based on air traffic control organization and geographic locations. With the increasing use of data applications for air-ground communications, the demand to effectively use the limited spectrum has increased. There are several proposed approaches to solve the projected saturated spectrum in the future. However, these approaches do not address the current practice of static spectrum allocation, which this author anticipates will be a major bottleneck for effective use of the limited spectrum. The current static channel assignment creates inefficient use of the limited spectrum. Regardless of whether a channel is used, it is permanently assigned to the particular geographical areas and organizations. This prevents other users from using the channels when the channels are idle. Also, this static allocation of the spectrum constrains the reassignment of channels and creates a long transition period for moving the existing analog system to a new digital system. The emerging Cognitive Radio (CR) technology provides the opportunity to address the static allocation of spectrum issue and offer a more flexible transition approach for updating the legacy air-ground radio system. The emerging CR technology provides the sensing of surrounding environment, allowing the radio to adapt to the environment accordingly. Built on software-defined radio (SDR) technology, CR is able to employ these features with the cognitive engine and the aid of several sensors. The cognitive engine carries out these tasks by obtaining all available information from sources such as sensors, protocol layers, a policy engine, and its own ha- - rdware, and then interprets, reasons, and makes the optimum decision to adapt. Integrated with ground radio stations and centralized management systems, the CR can dynamically use the available channels based on its actual location, environment condition, and, therefore, maximize the use of the limited spectrum.