Definition
On an engineering or maintenance drawing, short evenly spaced dashes used to represent edges, surfaces, or features of an object that are present but not directly visible from the chosen viewing angle.
Plain English
Dashed lines on a drawing that show parts of the object you couldn't see if you were looking at it from that side, like edges hidden behind another surface.
Context Anchor
Seen when reading aircraft maintenance drawings, parts diagrams, and blueprint views.
Derivation
Called 'hidden' because the lines stand in for features that are physically there but concealed from view in that particular drawing perspective.
Why Pilots Care
Correct interpretation prevents errors when locating internal fasteners, wiring routes, or structural members during inspection and repair.
Grounding Statement
If a feature is real but blocked from sight in that view, the drawing may show it with hidden lines.
Intuition Check
Hidden lines are not secret notes or optional marks. They are dashed drawing lines that show real features hidden from the current view.
Example Sentence 1
The hidden lines on the bracket drawing showed a bolt hole drilled through the back face that wasn't visible in the front view.
Example Sentence 2
Hidden lines on the wing rib diagram indicated the position of the spar web behind the skin.