Definition
A partial separation or fracture in a material that does not completely sever the part. In aircraft maintenance, a crack is a discontinuity in metal, composite, or other structure that may or may not be visible to the naked eye, and which can grow under repeated stress, vibration, or thermal cycling until it leads to component failure.
Plain English
A split or break in a part that hasn't fully separated yet. It might be tiny, but it can get worse over time and eventually cause the part to fail.
Context Anchor
Seen during preflight inspections, aircraft maintenance, logbook write-ups, and discussions of damage to metal, plastic, glass, composite parts, or engine components.
Derivation
Crack comes from older English words connected with a sharp breaking sound. That helps here because the aviation meaning is not just a mark you can see; it is a break or beginning of a break in the material.
Why Pilots Care
A crack in a load-bearing part can spread and cause sudden failure in flight.
Intuition Check
Do not assume a crack is just a cosmetic scratch. A scratch is a surface mark; a crack is a break in the material that may spread or weaken the part.
Example Sentence 1
During preflight, the pilot found a small crack near the exhaust stack and called a mechanic before the flight.
Example Sentence 2
Any visible crack in the propeller blade grounds the aircraft until repaired.