The high-stakes context of international radiotelephony (RT) communication, in which pilots and air traffic controllers (ATCOs) use aviation English (AE) as a lingua franca, requires a robust testing policy that is clear and fair to all stakeholders. The International Civil Aviation Organization Language Proficiency Requirements have been criticized for their lack of fit with pilots' and ATCOs' real-life communicative needs, for both native and non-native speakers of English (Douglas, 2014;Kim, 2012). This dissertation investigates and specifies the proficiency construct (awareness, knowledge, skills, and attitudes) in pilot-ATCO intercultural RT, following Fulcher and Davidson's (2007) test development framework, and drawing on theoretical and empirical studies in the domains of Aviation English, English as a Lingua Franca, Intercultural awareness, and Interactional competence. It is guided by the following overarching research