This paper attempts to analyze radiotelephony miscommunications from the standpoint of communication competence in pilots and air traffic controllers. Ineffective communication is frequently at the root of radiotelephony miscommunications. The objective was to describe the characteristics of communication failures between pilots and air traffic controllers and to examine the effects of communication incompetence to these patterns. Databases of communication and language related accidents as well as studies were reviewed and analyzed for patterns of miscommunication caused by insufficient language proficiency. Recurrent error patterns emerging from the analysis included unclear wording, ambiguities, partial or improper readbacks, and the use of mother tongue. The findings were to evoke the public's attention to English language proficiency and to provide practical information to facilitate the implementation of ICAO language proficiency requirements in Taiwan