Definition
On an aircraft drawing, a short symbol used to show that a portion of an object has been left out so the rest can be drawn at a useful size. A long break line is a thin ruled line interrupted by zigzags; a short break line is a thick freehand wavy line. The break line tells the reader, 'the object continues here, but it isn't shown.'
Plain English
A drafting mark that means 'part of this object has been cut out of the drawing to save space — assume it continues across the gap.'
Context Anchor
Seen in aircraft maintenance manuals, repair drawings, parts diagrams, and training material that show aircraft parts in a shortened or cutaway form.
Derivation
From the everyday sense of 'break' meaning a gap or interruption. The line marks where the drawing has been broken to skip over a section that doesn't need to be shown.
Why Pilots Care
Allows controlled separation during overload events so critical flight systems remain intact.
Analogy
It is like writing a long number as “123...789.” The dots show that something has been left out of the display; they are not part of the number itself.
Intuition Check
Do not read “break line” as a line where the aircraft part is broken. Here, it means a drawing line showing that the picture has been shortened or cut away.
Example Sentence 1
The drawing of the long wing spar uses break lines so the full length can fit on the page without losing detail at each end.
Example Sentence 2
The control surface separated cleanly along its break line during the overload test.