The advent of Instrument Landing Systems has allowed aircraft to safely takeoff and land in low visibility conditions. However, the lack of a means by which pilots can safely navigate on the ground in poor visibility conditions has been the cause of many runway incursions and several fatal aircraft accidents.
Currently flight crews use paper chart depictions of the airport surface and out-the-window visual cues to navigate on the surface. In addition they can be provided some feedback about their position on the surface from ATC. In clear, daylight environmental conditions flight crews can correlate airport features and navigation signs from the out-the-window view with the chart features to maintain airport surface situational awareness. In conditions of fog and darkness however, out-the-window cues are less available and it becomes a difficult task for flight crews to maintain situational awareness. Low visibility conditions also prevent ATC from tracking aircraft position on the airport surface from the tower
