This mixed-methods study investigated language anxiety among Korean military air traffic controllers (ATCOs) when communicating with native English-speaking pilots. The quantitative phase (N = 81) used hierarchical regression analysis examining relationships between individual characteristics and anxiety levels. The qualitative phase (N = 13) employed semi-structured interviews exploring controllers' experiences, anxiety triggers, and coping mechanisms. Results revealed that general communication anxiety ([beta] = 0.69, p < 0.001) and English proficiency ([beta] = -0.28, p < 0.05) significantly predicted anxiety with American pilots, with psychological factors explaining 58.8% of variance. These findings suggest that language anxiety stems from broader communication apprehension rather than isolated linguistic difficulties. Qualitative analysis identified five themes: communication breakdown, technical factors, skills hierarchy, informal coping, and institutional gaps. Overall, the study indicates that language anxiety in military ATC contexts is complex, influenced by individual psychological traits, situational demands, and organizational factors. It contributes to a deeper understanding of professional language anxiety in safety-critical contexts and provides evidence-based recommendations for aviation English training reform.