Air traffi c controller-pilot communications take place in a constrained but dynamic environment. They are usually highly scripted, brief, routine and, in most cases, unfold as expected. Sometimes miscommunications occur, and most of the time these miscommunications are easily resolved. Occasionally a miscommunication is not immediately resolved, or important information is not accurately conveyed in a timely manner. Even more rarely, a miscommunication results in an incident or accident. Because air traffi c controller-pilot communications are high-stakes interactions, such miscommunications, however rare, must be avoided insofar as possible so as to minimize the probability of an incident or accident occurring. For this reason, we believe it is important to take a proactive approach in examining the context in which these communications take place, for the purpose of understanding the conditions under which these interactions are most likely to be successful.