Transponder codes are four octal digit numbers transmitted by an aircraft transponder in response to a secondary surveillance radar interrogation. These discrete transponder codes (also known as squawk codes) help with the clear labelling of an affected aircraft on radar screens. Three particular squawk codes are associated with specific situations: 7500 for hijacking, 7600 for radio failure and 7700 for general emergencies, often related to medical or technical issues. In this paper, we analyse more than 800 trajectories received by the OpenSky Network over a two-year period as they were broadcasting the 7700 emergency code. Background information about the reason of these emergencies is taken from social networks and other crowdsourced information sources on the Internet. We provide an overview of various reasons for in-flight emergencies, typical trajectory patterns and communication strategies by airlines. Based on our semi-labelled dataset of trajectories, we also train models able to suggest possible explanations for trajectories when no information is available.