Anyone can look for cracks with the unaided eye. A small flashlight and mirror are all you need. There are three requirements:
1. Crack must be at the surface,
2. Crack must be large enough to be visible, and
3. Surface must not be covered with films that hide the crack.
You cannot detect cracks on surfaces that have a thick, flexible, powdercoat finish. That beautiful "automotive style" finish that is foreign to aircraft hides cracks. A less attractive, traditional, aircraft performance finish is easier to inspect. By performance I mean designed for function rather than cosmetic appearance. Each part has a role to play; performance paint films protect from corrosion without hiding defects.
