As described in Chapter 2, Aviation English comprises a variety of phrases which are used to convey specifi c information between pilots and air traffi c control (ATC) offi cers. For all pilots, the challenge is to learn what information needs to be communicated and at what point. They also need to ensure they place the required information in a predefi ned order, that all required information is included, and equally that unnecessary or redundant information is not transmitted. Further challenges include learning specifi c phraseology unique to aviation, as well as sentence structures that would be grammatically incorrect if employed in everyday conversation. These challenges are greater for pilots for whom English is a second language, who are at the same time learning or improving their English language skills. In this chapter, we discuss the challenges faced by native (NES) and non-native (EL2) speakers of English when they communicate over the radio using Aviation English in an operational environment. We draw on our studies of pilots in the Australian general aviation environment and we discuss the implications of the results of the research for the training of pilots and air traffi c controllers, who are all required to pass English language profi ciency tests. For pilots these tests examine their ability to communicate in conversational English and in situations requiring Aviation English. In contrast to conversational English, which commonly employs pauses and intonations, Aviation English is monotone, and most often presented in one short block without any pauses or breaks (Estival and Molesworth, 2009). Furthermore, all verbal communication between pilots in two different aircraft or between pilots and ATC are conducted using the radio, and, under such conditions, the use of information from facial expression, hand gestures and/or body position (i.e. body language), which have long been known to be crucial in effective communication (Mehrabian, 1972), are not available. In addition, as described in Chapter 6, environmental factors, such as workload (i.e. multitasking: fl ying plus communicating), work pressure (i.e. maintaining fl ight schedule) and the physical environment (i.e. temperature, hot or cold, and noise) are all known to adversely affect communication accuracy, especially for EL2 speakers.