Purpose: This study aims to examine the process of informal learning of aviation instructors. Design/methodology/approach: A qualitative instrumental case study design was used for this study. In-depth, multiple semi-structured interviews and document review were the primary approaches to data collection and the data were analyzed using constant comparative analysis. The Marsick, Watkins, Callahan, and Volpe reconceptualized model of informal and incidental learning underpinned this study. Findings: Findings support prior research on the catalysts, strategies, and lessons learned that are associated with informal learning. However, a key finding of this study was capturing the complexity of the informal learning process for aviation instructors as they faced the daily challenges associated with facilitating their students' learning which served as the catalyst for their learning. Research limitations/implications: The findings of this study are not intended to be generalizable to populations beyond this specific study due to limitations associated with the site selection, purposeful sample selection criteria, and sample size. Additionally, the unique nature of the aviation field and temporal considerations prevent the generalizability of the results of this study. Originality/value: Despite the growing base of research on informal learning, calls for research that continues to examine how certain characteristics of workers and their work environment influence informal learning, and research that provides more holistic understandings of this type of learning have been requested. This research responds to these calls by exploring the process of informal learning among aviation instructors. The catalysts for informal learning, the strategies used, and lessons learned are identified. More importantly, unlike previous research, the complexity of the process of informal learning is captured and illustrated as a cyclical, non-linear, non-sequential process that is highly intertwined with teaching in this aviation context. The careful documentation of the actual learning process provides thick, rich data to deepen our understanding of what this kind of learning actually looks like. (Contains 3 figures and 1 table.)