Definition
On an aircraft drawing, a line made up of long dashes alternating with pairs of short dashes, used to show the alternate position of a moving part, the position of a related part not actually present in that view, or a repeated detail that does not need to be drawn in full.
Plain English
A special dashed line on a drawing that shows something that is not really there in that view — like where a part moves to, or where another part would sit if it were shown.
Context Anchor
Seen on aircraft maintenance drawings, parts drawings, and installation diagrams.
Derivation
Called 'phantom' because the line shows something that is not solidly present in the drawing — a ghostly reference, like a part shown in a position it can move to, or a part that belongs there but is drawn somewhere else.
Why Pilots Care
When reading a maintenance manual or repair drawing, mistaking a phantom line for a solid object can lead to misreading what is actually installed versus what is only shown for reference.
Intuition Check
Do not read a phantom line as a solid part edge. It is a drawing convention that points out an alternate position, nearby item, or repeated feature.
Example Sentence 1
The mechanic checked the drawing and saw the flap shown with a phantom line in the fully extended position.
Example Sentence 2
Technicians followed the phantom lines on the drawing to locate the hidden rivet line behind the wing fairing.