Boroscopy
Borescopes are used for inspection work where the area to be inspected is inaccessible by other means. Source: Moritex USA Inc. An optical instrument used for inspection work where the area to be inspected is inaccessible by other means, borescopes can be rigid, flexible and semi-rigid.
A borescope is a visual inspection tool that has varied applications. The tool is commonly used in aircraft and helicopter maintenance. Comprising a rigid or flexible tube with a lens on one side and the display monitor on the other, borescopes are used to inspect hard-to-reach places of the turbine engine.