Definition
A very small hole, often barely visible, found as a defect in a coating, fabric finish, weld, casting, or sealed surface. In aircraft maintenance, pinholes are inspected for in painted finishes, doped fabric coverings, fuel tank seals, and welded joints, where they can allow corrosion, leakage, or loss of structural integrity if not repaired.
Plain English
A tiny hole, about the size of a pin prick, that shows up as a flaw in a coating or sealed surface and needs to be fixed.
Context Anchor
Seen during aircraft inspections, painting, fabric-covering work, composite repairs, sealant work, and leak checks.
Derivation
Pinhole comes from the idea of a hole about the size one might make with a pin. That helps the aviation meaning because the word describes the small size, not the importance of the defect.
Why Pilots Care
A pinhole can cause fuel leaks, loss of system pressure, inaccurate instrument readings, or fire hazards if left undetected.
Intuition Check
Do not assume a pinhole is harmless just because it is tiny. In aircraft work, the important question is whether it goes through a protective layer or lets something pass through.
Example Sentence 1
During the annual inspection, the mechanic found a pinhole in the fuel tank sealant and scheduled it for repair.
Example Sentence 2
A pinhole had developed in the altimeter diaphragm, causing the needle to fluctuate wildly in flight.