Plane sailing

Plane sailing (also, colloqually and historically, spelled plain sailing) is an approximate method of navigation over small ranges of latitude and longitude. With the course and distance known, the difference in latitude Δφ_AB between A and B can be found, as well as the departure, the distance made good east or west. The difference in longitude Δλ_AB is unknown and has to be calculated using meridional parts as in Mercator Sailing.