abstract:Prevailing visibility in aviation is a measurement of the greatest distance visible throughout at least half of the horizon, not necessarily continuously. To take the prevailing visibility, controllers reference a number of visual reference points: usually buildings, hills, or other geographic features.
Everyvesselshall proceed at a safespeedadapted to the prevailingcircumstancesandconditionsofrestricted visibility. A power-driven vessel will have her engines ready for immediate manoeuvre.