Definition
A line drawn on an engineering or technical drawing that duplicates an existing line in order to show the same feature on a different view, section, or sheet. It is used when a feature must be referenced in more than one place on the drawing without redrawing the underlying geometry.
Plain English
A line that is copied from one part of a drawing onto another so the same edge or feature can be shown in more than one view.
Context Anchor
Seen in older radar and electronic display discussions, especially when describing display faults or screen patterns.
Derivation
From the Latin 'tractus' meaning 'drawn' or 'pulled,' with the prefix 're-' meaning 'again.' A retrace line is literally a line that has been drawn again — copied from somewhere else on the drawing.
Why Pilots Care
A retrace line is not weather, traffic, terrain, or a navigation indication. Recognizing it as a display artifact helps prevent a pilot from treating a screen defect as real information.
Analogy
It is like moving a pen back to the left side of a page after writing a line. If the pen is still touching the paper during the move, it leaves an extra line that was not meant to be part of the writing.
Intuition Check
Do not read retrace line as a flight path flown back over the same route. Here, it means a visible return path on an electronic display.
Example Sentence 1
The technician used the retrace line on the second view to confirm the bracket's edge matched the position shown on the main assembly drawing.
Example Sentence 2
The pilot marked the retrace line on the sectional so they could return safely if weather moved in.