As we have stated in the past, Nondestructive testing (NDT) covers a wide variety of techniques the most efficient and accurate of which is the use of ultrasonic inspection equipment such as ultrasonic emersion tanks. These systems, when used by trained professionals, can give the operator detailed information that can save owners money and help make the public safer. However, even though less accurate the visual inspection of parts and systems still serves a role in aircraft maintenance. Here are some of the optical aids that are used in visual inspection.

  • Microscope: Magnifying devices and lighting aids can and are used to aid in the visual inspection of objects and materials. These devices can be used to check for the presence of foreign objects, corrosion and damage. With these kinds of devices it is useful to have a general idea of where the defect may be located.
  • Borescope: A borescope is an optical device consisting of a rigid or flexible tube with an eyepiece or display on one end, an objective lens or camera on the other linked together by an optical or electrical system. Generally, the diameter of the borescope depends upon the diameter of the hole or bore to be inspected. Rigid borescopes have the limitation that access to what is to be viewed must be in a straight line. Ultrasonic inspection does not have this limitation.
  • Endoscope: An endoscope is much like a borescope except that it has superior optical systems and uses a strong light source to aid it. Endoscopes are also unique in that objects remain in focus from about 4mm on. Most people are familiar with the medical applications of this technology.
  • Holography: Holography is the name given to the method of creating a three-dimensional image of any given object. Holography is used in NDT to provide a record of the image of an entire surface which can be compared to a defect-free surface.

As you can see, the visual inspection of objects goes far beyond an observer using only his or her naked eyes to spot problems with materials and objects. If this were the case, it would not be very useful to mechanics and engineers as the human eye is quite weak compared to instruments that can aid it. The ultrasonic testing and inspection of materials and objects goes further by creating a detailed record without many of the limitation inherent in other NDT methods.