Checking for Integrity: Non-Destructive Inspection Technicians

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A Marine conducts a non-destructive inspection (NDI) on an MV-22 Osprey aboard amphibious assault ship USS Boxer (LHD 4).
By Naval Air Force Atlantic Public Affairs                                                              

Aviation maintenance is a highly diverse and technical field comprised of a variety of skill sets. Non-destructive inspection (NDI) technician is one of many such specialties within the aircraft structural mechanics (AMs) rate.

NDI technician is not a rate by itself, but a part of the AM rate, and responsible for performing structural integrity checks on aircraft components. AMs play a vital role in all levels of aviation maintenance. At the squadron level (organizational level), they are responsible for the upkeep of aircraft structural components, as well as all hydraulic and tire and wheel systems. Fleet Readiness Centers (intermediate level) perform specialized repair of structural subcomponents. These special NDI skills require Sailors to receive additional advanced technical training. When they complete this training, graduates earn a special Navy Enlisted Classification, which they retain throughout their enlisted naval careers.

Non-destructive inspection gets its name from the manner in which inspections are completed. Inspections are performed on metal or composite items using six different methods, depending on the type of part to be inspected and technical requirement.

The first method used to identify surface defects is known as fluorescent penetrant inspection. Fluorescent liquid is highly sensitive to black light when it is applied to a clean surface of a metal part. The liquid is allowed to dwell on the part for a set period of time to ensure it settles into any surface discontinuities. Once the excess liquid is removed, any remaining liquid that puddles on the surface may be a sign of an unacceptable condition.

Next method is visual inspections, where digital micrometers and borescopes allow the technician to look inside certain parts without disassembling or damaging the parts.

Another useful inspection for surface and near-surface defect detection is the eddy current inspection technique. This method uses a probe that emits a small electromagnetic field. As the field interacts with the surface area of the inspected part, it detects changes in material density. These changes can be interpreted as indications and viewed on the screen of the test unit.

Magnetic particle inspections help detect surface and subsurface defects of ferrous metals, which is ideal for steel components. A magnetic field is produced within the part by a magnetization process. If defects are present, they will form smaller magnetic fields that can be seen with the use of fluorescent ferrous metallic media and a black light.

The ultrasonic inspection technique works in much the same way as it would if one went to the doctor’s office. This method detects indications with the use of ultra-high frequency sound induced into the part. The propagation of the sound through the part can be read using a visual unit. This is the primary means for inspecting composite materials.

Finally, the radiographic inspection brings the power of X-rays into detecting inner part defects. The exposed radiographs are viewed and inspected using digital processing.

With its unique niche within the AM community, NDI offers Sailors a challenging career field.