Definition
In an aircraft engineering or technical drawing, a short-dashed line used to represent an edge, surface, or feature that exists on the object but is not directly visible from the viewpoint shown — for example, an internal bore, a hole on the far side of a part, or a structural member concealed behind another surface.
Plain English
A dashed line on a drawing that shows the outline of something you couldn't actually see if you were looking at the part — because it's behind, inside, or on the other side.
Context Anchor
Seen on aircraft maintenance drawings, parts diagrams, and other technical illustrations where the drawing must show features that are not visible from the outside view.
Why Pilots Care
Allows technicians to understand the full structure of components from 2D drawings without needing to disassemble the aircraft.
Analogy
It is like drawing a dashed outline of an object behind a wall to show that it is there, even though the wall blocks your view of it.
Intuition Check
Hidden Line does not mean a line that is secret or accidentally hard to see. In drawing use, it means a dashed line intentionally added to show a feature that exists but is not visible from that view.
Example Sentence 1
The technician traced the hidden line on the diagram to locate the bolt hole on the back side of the bracket.
Example Sentence 2
When reading the engine blueprint, pay attention to the hidden lines indicating the positions of the internal baffles.