Definition
A small hole drilled at the very tip of a crack in a metal aircraft skin or structure to prevent the crack from spreading further. The hole removes the sharp point where stress concentrates, which is what allows a crack to keep growing under load and vibration.
Plain English
A tiny hole drilled at the end of a crack to stop it from getting longer. By rounding off the sharp tip of the crack, the metal no longer has a weak point that wants to keep tearing.
Context Anchor
Seen during aircraft inspection or maintenance discussions, especially when checking outer wing surfaces, tail surfaces, skin, fairings, or other parts for cracks.
Derivation
The name describes exactly what it does: a drill used to stop something. The term has been used in metalworking and aircraft repair for decades to describe this specific anti-cracking technique.
Why Pilots Care
Stops small cracks from growing into larger ones that could weaken the airframe and lead to in-flight structural failure.
Analogy
Think of a small tear at the edge of a piece of paper. If you keep pulling, the tear runs further. Punch a clean round hole right at the end of the tear and the paper resists tearing past it. A stop-drill works the same way on metal.
Intuition Check
Stop-drill does not mean to stop using a drill. In this context, it means to drill a small hole that helps stop a crack from growing.
Example Sentence 1
During the preflight inspection, the mechanic pointed out a stop-drill near a small crack in the wingtip fairing and noted it in the logbook as a temporary measure.
Example Sentence 2
Several stop-drilled holes were visible along the fuselage, showing where earlier cracks had been arrested.