<p>  </p> <p>Although airports of all sizes have incorporated sustainability practices into planning, there is a gap in literature concerning the impacts of sustainability initiatives on airport operations and stakeholders. This multiple case study sought to explore the impact assessment methods used by six small hub airports (cases) that received the Federal Aviation Administration (FAA) airport sustainability Airport Improvement Program (AIP) grants to prepare airport sustainability planning documents.</p> <p>The objective of the study was twofold. The first objective was to gain in-depth understanding of sustainability metrics and Key Performance Indicators (KPIs), and sustainability impact assessment methods and tools used by small hub airports. The second objective was to develop a preliminary framework for assessing the impacts of sustainability initiatives in airports. Three types of data were collected airport sustainability planning documents, archival records, and interviews with 14 airport executives and two airport planning consultants. Sustainability planning processes, sustainability assessment methods and tools, and sustainability metrics and KPIs were identified from data for each case and compared to one of the most comprehensive industry-specific airport sustainability rating systems, the Airport Cooperative Research Program (ACRP) <em>Report 119: Protype Airport Sustainability Rating System: Characteristics, Viability, and Implementation Options</em>. Interview responses from airport executives and consultants were used to corroborate information in the sustainability planning documents.</p> <p>The findings of this study showed more commonalities than differences in the approaches to sustainability impact assessment by the six small hub airports in this study. Commonalities were evident in the criteria for selecting sustainability initiatives, indicating that cost and return on investment were the major factors. In addition, small hub airports in this study reported similar challenges on tracking sustainability metrics and KPIs, indicating that more work is needed in this area. The differences noted were driven by airport operating conditions such as geographical location and local community goals. </p>