Visual inspection is the oldest and still often the principal method used to identify degradation or defect in aircraft systems or components. Good eyesight is of prime importance in visual inspection. Aircraft maintenance engineers may use magnifiers and bore scopes to enhance their visual capabilities. Although the engineer’s vision is important, he also has to make judgements about what he sees. To do this, he brings to bear training, experience and common sense. Thus, reliable visual inspection requires that the engineer first sees the defect and then actually recognises that it is a defect. Of course, experience comes with practice, but telltale signs to look for can be passed on by more experienced colleagues.