Definition
A line drawn on a navigation chart along which an aircraft's position is known to lie at a given moment, derived from a single navigational observation such as a bearing, range, or celestial sight. A single position line shows direction or distance to a known reference but does not by itself fix the aircraft's exact location; two or more position lines crossing each other produce a fix.
Plain English
A line on a chart that tells you 'somewhere on this line is where you are right now.' One line narrows it down; two crossing lines pinpoint where you actually are.
Context Anchor
Used in pilot navigation when plotting where the aircraft is on a chart, especially when using landmarks, radio signals, or measured directions.
Derivation
Combines 'position' (placement or location) with 'line' (a straight path or mark); the aviation sense emphasizes a line of possible locations rather than a single point.
Why Pilots Care
Intersecting two or more position lines produces a reliable fix, essential for confirming location when visual references are limited.
Analogy
Like knowing you are on a particular highway but not yet knowing your exact mile marker.
Intuition Check
Do not read “position line” as the line showing where you plan to fly. It is a line showing possible present locations of the aircraft.
Example Sentence 1
He took a bearing from the VOR and drew the position line on his chart, then crossed it with a DME arc to get his fix.
Example Sentence 2
Two crossing position lines gave the crew a precise fix over the lake.