Definition
A surface defect in sheet metal where the shape, edges, or fasteners of an underlying structure show through as visible lines, ridges, or impressions on the outer skin. It is most often seen on aircraft skins where rivets, stringers, ribs, or doublers beneath the surface become faintly outlined on the exterior, especially after painting or under certain lighting.
Plain English
When the shape of something underneath a metal panel shows through on the outside — like seeing the outline of ribs or rivets faintly on the aircraft's skin.
Context Anchor
Seen during aircraft painting, fabric-covering work, composite repair, or inspection of a repaired surface.
Derivation
From the old telegraph system, where a signal sent at one end appeared at the other. Here, the shape of a hidden part 'sends a signal' through the skin and shows up on the outside.
Why Pilots Care
Indicates loose or damaged fabric that can affect flight characteristics and must be repaired before flight.
Analogy
It is like painting over a wall patch and later seeing the outline of the patch through the paint. The patch is covered, but its shape still shows.
Intuition Check
Telegraphing does not mean sending a message by radio or wire here. It means an underlying shape is showing through the aircraft’s outer finish.
Example Sentence 1
After painting the fuselage, slight telegraphing of the rivet lines was visible along the upper skin.
Example Sentence 2
Telegraphing appeared after the fabric had been tightened too much during covering.