AIS gaps is a term referring to a period of time when signals from an AIS transponder are not received and the vessel’s movements and position are unknown. However, that does not mean all vessels with transmission gaps should be flagged. The vast majority of AIS transmission gaps worldwide are not deliberate. The most common reason for gaps in AIS transmissions is that they are simply not detected by any sensor. This can be caused by poor coverage, signal collision, weather conditions or GPS jamming. A vessel that deliberately goes dark, on the other hand, has decided to stop transmitting, probably to conceal what it’s up to.