What does the term "stop drilling" refer to in aviation repair?

The term "stop drilling" is specifically used in aviation repair to refer to the practice of drilling a small hole at the ends of a crack in a material, such as metal in an aircraft structure. This technique is employed to prevent the crack from spreading further due to stress or fatigue. By introducing a hole at each end of the crack, it effectively changes the stress distribution around the crack, thereby stopping its progression and allowing for repair work to be carried out without the risk of further damage.

This is an important method in structural maintenance and repair, as it helps ensure the integrity of the component until a more permanent repair can be made. The other options, while they involve drilling, do not relate directly to the specific function of mitigating crack propagation, which is the emphasis of the "stop drilling" technique.