What are the qualification requirements for general aviation personnel that perform NDT to support in-service inspection? Despite guidelines, the answer remains unclear.

For years I have had the opportunity to attend aerospace sponsored seminars and conferences that promote continued proficiency for general aviation.

The conferences are always informative, add value to the experience level of the attendees and focus on the issues at large. As a continuance of becoming more aware of industry issues, the qualification requirements of personnel performing nondestructive testing (NDT) to support general aviation require discussion. So, what are the issues with existing practices?

To answer the question, it is important to step back and understand the life cycle of a part that becomes attached to or installed onto an aircraft. Second, it is important to explore not only the domestic but also the international positions on this subject.

Part Life Cycle

When materials are initiated for use on an aircraft, the process starts with the raw material specified by engineering design followed by the manufacture and processing of finished machine parts to a drawing or specification. This phase is extremely critical in that the engineering requirements are validated by NDT prior to part exposure to design conditions on an aircraft. The personnel that perform nondestructive testing at this stage must have a commanding knowledge of materials and an understanding of the unique and inherent processing flaws. In addition, they also need to have a commanding knowledge of manufacturing processes and their associated flaws. The NDT inspector is responsible for the identity of each flaw, categorization and making acceptance disposition based on a library of industry and prime contractor specifications. It should be noted that the inspectors commonly inspect several product forms (castings, forgings, wrought materials, welds...) to a wide array of customer requirements on a daily basis. Chart 1 on page 25 identifies a partial listing of common discontinuities identified during the manufacture phase.

The qualification requirements for NDT personnel that support the manufacturing stage are defined in Aerospace Industries Association (AIA) document NAS 410. For personnel to accept parts at this stage, they must be certified by the employer. Prior to certification, certain qualification requirements must be met. Chart 2 on page 26 provides training and experience requirements.

After the finished machined parts are validated with NDT, they are certified for flight use, installed on the aircraft and start their service life.

Based on part design function and importance to flight safety, they are periodically re-inspected to assure in-service stresses have not degraded or challenged the projected design life. Common discontinuities associated with in-service conditions include: heat damage, corrosion, stress cracks, erosion/wear and composite disbond.

It should be noted that flaws associated with in-service inspection are narrow in scope, well defined and the procedure for their detection is usually outlined in methodical manufacturer developed inspection procedures using specific equipment and materials. Unlike manufacturing inspection, in-service inspections are very prescriptive and require minimal interpretation regarding inspection methodology or part acceptance. This stage is extremely important in that failure to identify degradation, could lead to loss of aircraft or, more importantly, loss of life.

Domestic Programs

For ease of comparison, in-service inspection of aircraft can be grouped into two categories — air carrier and general aviation. For inspection performed to support air carriers, FAR Part 121 (121.133 & 121.135) is the governing document and places the responsibility on the air carrier to develop the required procedures to assure personnel are properly qualified. In response to FAR 121, the Air Transport Association developed ATA 105 to address the training and qualification of NDT personnel. This document defines the following qualification criteria for NDT personnel to make unrestricted acceptance/rejection dispositions. See Chart 3, at left.

ATA 105 recognizes the narrow scope and prescriptive nature of in-service inspection and has provisions to reduce the required training and experience hours. The narrow scope reduction has resulted in certification level — Level I Special.

The narrow scope permits the number of training and experience hours to be reduced on a case by case basis by the employer but in no case may the number of training hours be less than 25 percent nor the number of experience hours be less than 10 percent of the minimum required for Level 1 in the applicable method.

International Programs

The research performed on this subject is primarily based on aviation activities within the European Union. The European Federation of Nondestructive Testing (EFNDT) recognizes the mandate of EASA Part 145 of which further mandates EN 4179-2005 for the aviation maintenance sector. This includes any aircraft that flies not just the air carriers. EN 4179-2005 parallels NAS 410 (See Chart 2) regarding qualification requirements but also has provision for a Level I Limited similar to the Level I Special addressed in ATA 105.

The preceding overview addressed NAS 410 and EN 4179 — both of which are applicable to the design and manufacturing of new parts and components. It also addressed ATA 105, a document designed for commercial aviation.

All of these documents have roots to the recommended practices of the American Society For Nondestructive Testing (ASNT) document SNT-TC-1A.

Clarity Needed

So what are the qualification requirements for general aviation personnel that perform NDT to support in-service inspection? To this point, the answer is unclear. There have been guidance letters issued by the FAA that summarize the preceding and recommend the NDT organization use as a reference. While each of the preceding standards may be cherry picked for applicability, they do not address the specific needs for general aviation.

The FARs provide minimal guidance so there is a wide range of interpretation as to applicability. The range of interpretation and application stems from the FARs that permit NDT to be conducted if it is a part of the maintenance, preventative maintenance or alteration of an aircraft by non-NDT certificated personnel. This activity is accomplished at the most important stage of a parts life — after design function is exercised and repeated stresses are induced as a result of flight service. See Chart 4 on page 28.

All of this being said doesn’t mean that the sky is falling. The tools for proper training are available through Web-based training, computer-based training, self study, consultants specializing in training and training that is periodically offered at safety seminars. But, the issue remains that a specific industry conscious standard for general aviation personnel does not exist. It is recommended that such a standard be developed. This standard should identify the narrow scope performed during in-service inspections and should recognize a reduced scope certification similar to both ATA 105 and EN 4179-2005.

Development of such a standard can be accomplished based on the input of industry. To comment or become a committee member on the development of such a standard, please contact the author at bobpotter@metalfinishingco.com