NAS410 explained: aerospace NDT certification, Levels 1 to 3

NAS410 (also written NAS 410) sets the minimum requirements for qualifying and certifying the people who perform nondestructive testing (NDT) — or NDI or NDE, which it treats as the same thing — in aerospace manufacturing, service, maintenance and overhaul. It is a National Aerospace Standard published by the Aerospace Industries Association (AIA), and it is kept technically equivalent to Europe's EN 4179, which is why aerospace NDT certification reads much the same on both sides of the Atlantic.

Unlike SNT-TC-1A, NAS410 is not a set of recommendations. Its hours, scores and intervals are minimums. An employer may add levels, raise requirements or take on a prime contractor's extra rules, but it cannot go below the standard.

Who it applies to

NAS410 covers anyone who uses NDT to test or accept aerospace material, parts or assemblies; who is directly responsible for the technical adequacy of the methods and equipment; who operates automatic interpretation systems; who approves NDT procedures or work instructions; who audits NDT facilities; or who provides technical NDT support or training (1.2.1). It does not cover people with only administrative or supervisory authority over NDT staff, or researchers developing a technique for a certified Level 3 to approve later.

Revision 6 carries detailed requirements for seven methods: eddy current, penetrant, magnetic particle, radiographic, shearography, thermographic and ultrasonic testing (1.2.3). Other methods — acoustic emission, neutron radiography, leak testing, holography — come under it when engineering, quality or the prime contractor invokes it, with hours set by the Responsible Level 3 by comparison with a method of similar complexity (6.4).

Responsibility runs down the supply chain. The employer implements the standard and certifies its people, and the prime contractor is responsible for its sub-contractors' compliance (4.3.1). That is why so many aerospace suppliers work to a prime's supplement on top of NAS410, and why their written practice has to carry any requirements the prime or cognizant engineering organization adds (4.1.2).

The written practice and the Responsible Level 3

Every employer keeps a written practice covering its levels, duties, training and experience, certification and recertification, records, what suspends, revokes and reinstates a certification, and its annual proficiency review. It also names the techniques within each method, the training outlines, who administers exams and how many questions they carry, and the vision test method used (4.1). It is approved by the Responsible Level 3 and must be available to the employer's customers and regulators.

The Responsible Level 3 is the one person the employer designates in writing to act for it on qualification and certification. They are a NAS410 Level 3 in at least one method, know the employer's specifications, products and techniques thoroughly, and control the training and exam program, including approving Examiners, instructors and outside agencies (4.3.2). Other Level 3s can be designated as Examiners to cover methods the Responsible Level 3 does not hold.

The Responsible Level 3 may come from an outside agency, but then they can only qualify people: only the employer can certify them, and no employer can certify for another. Nobody qualifies themselves, though a self-employed person can certify themselves once another NAS410 Level 3 has qualified them and they keep a written practice (4.3.1, 4.3.3).

Levels 1-Limited, 1, 2 and 3

NAS410 writes its levels in Arabic numerals, and Revision 6 has four, plus the trainee (section 5):

• Trainee — documented in a training program for a stated period, gaining experience under direct observation of a Level 2 or 3 (or a Level 1 or instructor if the Responsible Level 3 approves). No accept or reject decisions, and nothing done independently.
• Level 1-Limited — one specific test on a specified part, feature or assembly, each approved by the cognizant engineering organization, with no more than three held at a time and recertification every two years (Appendix B).
• Level 1 — follows work instructions, processes parts, standardizes equipment and records results. May interpret and accept or reject specific products only when the written practice says so and the Responsible Level 3 approves.
• Level 2 — sets up and standardizes equipment, interprets and evaluates for acceptance, guides trainees and Level 1s, and may write work instructions from approved procedures for a Level 3 to approve.
• Level 3 — interprets codes and contracts, takes technical responsibility for the facility and staff, selects methods and techniques, approves procedures and work instructions, and provides or directs training, examination and certification. A Level 3 accepts parts only if their practical exam proved they can.

Section 5 also describes the Auditor: employer personnel designated by the Responsible Level 3 to perform technical NDT audits. It is a designation with its own knowledge requirements, not a rung above Level 3, and it carries no authority to examine or certify anyone.

Training and experience

Formal training comes before, or alongside, on-the-job training, to an outline the Responsible Level 3 or Examiner approves (6.1). Revision 6's minimums, in our own layout:

Around those numbers:

• Refresher training is required for anyone credited with earlier training, or not certified within twelve months of their training (6.1.3).
• Earlier training and experience under NAS410, EN 4179 or another recognised program can be accepted, in whole or in part, once the Responsible Level 3 or Examiner documents its equivalence (6.1.4, 6.3.3).
• Experience is overseen by a Level 2 or 3 in the method, and a trainee's record shows the date, the activity, the hours and who was observing (6.3.1).
• Radiography candidates are trained on radiation hazards and the applicable regulations before certification (6.1.5).
• Level 3 requires prior Level 2 in the method. Table 5 sets the Level 2 experience needed first: four years with no college study, two with a two-year engineering or physical science program, one with a three-to-four-year degree. Revision 6 adds Appendix D, a competency-based points route to Level 3 eligibility as an alternative to Table 5.

Exams

Each method has a general, a specific and a practical exam, and Level 3 candidates first pass a basic exam, once (section 7):

• Basic (Level 3 only): three sections — at least 10 closed-book questions per method on at least four methods, 10 on materials and manufacturing processes, and 10 open-book on NAS410/EN 4179 itself — each passed at 80%. It is a prerequisite and does not count toward the composite.
• General: closed book, at least 40 questions at every level. A current ASNT, ISO 9712 or national aerospace NDT board qualification can satisfy it where the written practice allows.
• Specific: open book, at least 30 questions, on the employer's own specifications, procedures, equipment and products. It is given only after 75% of the experience minimum is complete.
• Practical: after all of the experience. Levels 1 and 2 inspect at least two test samples of differing configurations per method, which the candidate has not seen before; Level 3 writes a procedure or work instruction, plus a Level 2-style hands-on practical if they will accept parts.
• Scoring: at least 70% on each exam, every specified discontinuity found on the practical, and an average of at least 80%, with exams weighted equally (7.2.3).
• Retakes: documented additional training first, at least 25% new questions, different test samples, and within the written practice's limit, which may not exceed six months (7.2.4). Failing a recertification exam suspends the current certification.

Exams are administered and graded by the Responsible Level 3 or an Examiner certified in the method, who may delegate multiple-choice administration in writing. Nobody may be examined by themselves or by a subordinate, and written exams may not be translated verbally (7.1.1, 7.2.1).

Vision

Near vision is checked every year and color perception at least every five years, before first certification and after anything that could affect sight (7.1.2). Revision 6's Table 7 gives three near-vision options — Jaeger No. 1 at not less than 12 inches, Snellen 20/25 at 16 inches (plus or minus an inch), or the Tumbling E test of ISO 18490:2015 — in at least one eye, natural or corrected, with no simulated tests. Snellen and Jaeger tests are given by trained people the Responsible Level 3 designates, or by qualified medical staff. Anyone who needs correction to pass wears it for every inspection. Vision requirements do not apply to instructors or auditors.

Keeping a certification

Levels 1, 2 and 3 are recertified at least every five years — Levels 1 and 2 by specific and practical exams, Level 3 by the same or by the Appendix A credit system, which needs Level 3 work in the method, eight verifiable Level 3 tasks and 24 points of professional activity over the period (8.5, Appendix A). In between:

• Annual proficiency review: a documented yearly check of technical proficiency in each method, for everyone processing or inspecting product (8.6).
• Suspension follows an expired vision exam or proficiency review, twelve consecutive months without working in the method, a failed recertification exam, or deficient performance (8.3.2).
• Revocation follows 24 consecutive months without working in the method for the employer, the end of employment, or technical incompetence; unethical conduct revokes every certification (8.3.3).
• Reinstatement: a suspension is lifted once its cause is corrected and proficiency verified; an expired certification comes back only by specific and practical exam, and a revoked one by general, specific and practical (8.4).
• Month-end expiry: certifications, vision exams and the proficiency review all expire at the end of the month in which they fall due (8.3.1).

Records are kept for as long as the certification is in effect: the latest exams and practical checklist, previous scores, training and experience history, education used to qualify, current vision results, the authorising signature and the latest proficiency review, and the reason and date of any suspension or revocation (8.2.1). Employees are entitled to all of it except the exams themselves.

If you are accredited for NDT through Nadcap, your program is audited against NAS410 and your customers' requirements — the Nadcap NDT guide covers preparing for it. For how NAS410 sits beside the general-industry schemes, see the comparison.

Frequently asked questions