Definition
A charted pair of fixed marks, one low and near and one higher and further back, that when kept in line define a safe approach track through a channel or over a bar. The chart states the leading line's true bearing, for example 047 degrees, and the marks are frequently lit for night use. Sensitivity to lateral error increases with the separation of the marks and decreases with distance off, so a leading line is most precise close in and should be abandoned beyond its charted limit.
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