Evaluating Your NDI Services

The nondestructive inspection provider audit explained.

The use of nondestructive inspection (NDI) has ballooned in the last few decades as new materials have evolved for use in today’s aircraft. As we explore the frontiers of materials development, NDI has kept apace not only by allowing inspection of advanced materials but allowing continued inspection of older aircraft. NDI has benefited greatly by miniaturization and computer technology. However, the basics of NDI services evaluation remain: determination of the ability of the service organization to meet the aircraft’s maintenance program requirements.

Every audit or evaluation begins with preparation. It includes the logistics of the visit to include dates and contacts. If an audit checklist is going to be used, the auditor may provide the standard he intends to use. In certain cases a customized checklist may be developed internally for focused evaluations. This may be necessary to assure that the provider has the necessary tooling and expertise to meet specific maintenance program requirements covered in an approved aircraft NDI manual. This is useful if key Airworthiness Directive (AD) work is anticipated.

The audit of an NDI organization focuses on five standard elements:

  • Facility or environmental conditions
  • Tooling
  • Personnel certification
  • Tech data or work instructions
  • Training

Facility requirements

NDI organizations may have minimal need for structured facilities. There may only be sufficient brick and mortar to house equipment, administration, and records. Equipment storage in the facility should demonstrate good housekeeping and organizational layout. Poor housekeeping in any audit is an indicator that environmental disciplines are wanting and warrants a closer look around. Well-organized work spaces and tooling are positive indicators of a well-managed and disciplined workplace. Tooling and training records, areas requiring good organization should be carefully scrutinized.


Tooling is the point of NDI. Depending on the techniques used and the repair station’s authorizations the equipment may be extensive. Much of it is subject to calibration standards and should be listed in the calibrated tooling program. Annual calibration is normal but in some cases tooling may be self-calibrating. Ultrasonic inspection, for example, is checked against a physical calibration standard prior to use in an inspection. A calibration program will describe these details – the auditor should compare the repair station’s program to the tooling in review. In cases where the owner/operator’s maintenance program requires more conservative tooling calibration controls, he should inform the service provider of the requirements. In discussing tooling we focus on the most common NDI methods.

Eddy current (ED)

  • Probes – Should be the right design and frequency. In preparing for the audit the auditor should have a list of tooling that would be required for use on their aircraft. Probes should be on that list. If the service is using equivalent probes be sure they have the records to determine equivalency and that technical data allows the probe.
  • Cables – Be sure they are properly labeled, that they are in good condition. (No fraying, exposed shielding or loose connections.)
  • ED test box – The unit should be free of damage and in good condition. Calibration should be current. The test box should be a model that is applicable to maintenance program inspection. If it has been determined to be equivalent, the means of determining equivalency should be evaluated.

Ultrasonic (UT)

This content continues onto the next page...

We Recommend