Nondestructive testing (NDT) is one of aviation maintenance's most powerful tools, allowing technicians to detect cracks, corrosion, delaminations, and other hidden defects without damaging the part being inspected. But the value of any NDT method—whether magnetic particle, dye penetrant, radiography, ultrasonic, or eddy current—depends almost entirely on the competence of the person performing it. A probe moved too quickly, a gain setting chosen incorrectly, or a report written ambiguously can allow a life-threatening defect to go undetected. That is why the aviation and aerospace industries have developed a formal, tiered qualification and certification structure for NDT personnel.
In the United States, the dominant standard governing NDT personnel qualification in aerospace is NAS 410, published by the National Aerospace Standards Committee of the Aerospace Industries Association (AIA). NAS 410 establishes minimum requirements for training, experience, examination, and certification of NDT Level I, Level II, and Level III personnel across the most common aerospace NDT methods. The FAA recognizes NAS 410 as an acceptable means of compliance when contractors and repair stations need to demonstrate that their NDT workforce is qualified, and it provides useful background knowledge for AMTs, though the specific certification levels and hour requirements go beyond what is directly tested on the FAA Airframe/Powerplant knowledge, oral, and practical exams.
The Three-Level Qualification Framework
NAS 410 organizes NDT qualification into three distinct levels, each representing a progressively deeper combination of knowledge, skill, and responsibility. Understanding what each level can and cannot do is critical both on the job and on the knowledge test.
Level I — Performing Under Supervision
A Level I technician is qualified to set up and calibrate NDT equipment and to perform specific tests according to written procedures—but only under the direct supervision of a certified Level II or Level III. The Level I does not independently interpret or evaluate test results. Instead, findings are passed up to a higher-level certifier who makes the accept/reject determination. Think of Level I as a skilled operator who can precisely follow a recipe but is not yet authorized to change the recipe or decide whether the final product is acceptable.
Because Level I personnel work strictly within approved procedures, the written instructions they follow must be detailed enough that a qualified technician can perform the test consistently with minimal judgment calls. If any ambiguity arises—unusual geometry, a borderline indication, equipment behavior outside tolerance—Level I must stop and consult their supervisor.
Level II — Independent Performance and Interpretation
A Level II technician can set up equipment, perform tests, and interpret and evaluate results in accordance with applicable codes, standards, and specifications. Level II personnel may also write testing procedures (though in some organizations that authority is reserved for Level III), train and guide Level I technicians, and prepare test reports and documentation. The Level II is the workhorse of an NDT shop—capable of completing the full inspection cycle from setup to a documented accept/reject decision.
Because Level II personnel are making safety-critical accept/reject calls, their qualification requirements are substantially higher than Level I, including more documented training hours, more on-the-job experience hours in the specific method, and a more comprehensive written and practical examination.
Level III — Technical Authority and Program Oversight
A Level III is the highest qualification level and carries the broadest technical authority. Level III personnel can perform all Level I and Level II functions, and additionally are responsible for establishing and approving NDT procedures, interpreting codes and standards, and directing the overall NDT program within an organization. They may also design training curricula, administer qualification examinations, and certify personnel at Levels I and II. Because this role requires mastery of NDT principles as well as regulatory and organizational knowledge, the qualification path to Level III is the most demanding of all three levels.
Training and Experience Requirements
NAS 410 specifies minimum hours of training and on-the-job experience for each NDT method and each certification level. The exact hour requirements vary by method—for example, ultrasonic testing generally demands more training hours than liquid penetrant testing because of its greater technical complexity—but the structure is consistent across methods.
Training hours refer to formal instruction, which may be classroom, laboratory, or a combination of both, delivered by a qualified instructor. Training must cover the physical principles behind the method, equipment operation, materials and their properties relevant to the method, applicable standards, and procedural requirements.
Experience hours refer to actual on-the-job time performing that specific NDT method on real hardware or representative test specimens, accumulated under the supervision of someone at a higher certification level. These hours must be documented and verifiable; self-reported undocumented hours are not acceptable under NAS 410.
Importantly, NAS 410 allows training and experience hours to be accumulated across more than one employer, provided adequate documentation exists. An AMT who completed NDT training at a previous shop and has the records to prove it can apply those hours toward certification at a new employer.
Examination Requirements
Before certification at any level, candidates must pass a set of qualifying examinations administered by or under the authority of the employer's Level III or an authorized examining body. NAS 410 requires three distinct examinations:
- General examination: Covers the fundamental principles of the NDT method, including the physics involved, equipment theory, and the factors that influence test results. This written exam applies to every method a candidate seeks to be certified in.
- Specific examination: Focuses on the particular procedures, equipment, and standards used within the certifying employer's operation. Because different organizations use different equipment configurations and apply different acceptance criteria depending on the customer or contract, the specific exam is tailored to what the technician will actually encounter on the job.
- Practical examination: Requires the candidate to demonstrate hands-on proficiency—setting up equipment, performing a test, and (for Level II and above) interpreting results on actual or representative test specimens containing known natural or artificial defects. A passing score on the practical exam is especially important because NDT is fundamentally a skill-based discipline.
Passing score requirements for these examinations are defined in the employer's written practice consistent with NAS 410, and can vary by method, level, and organization rather than following one universal flat percentage across the board.
Certification, Recertification, and Vision Requirements
Certification under NAS 410 is granted by the employer, not by the government or a third-party body (unless the employer delegates examination to an authorized NDT training school). This is an important distinction: the employer's Level III holds the technical and administrative authority to certify personnel, and that certification is valid for the methods and levels specified in the certification document.
Recertification is required periodically, with the maximum interval and interim requirements (such as periodic vision checks) defined by the applicable NAS 410 revision and the employer's written practice; technicians must demonstrate continued proficiency—typically through re-examination—to remain certified. Level III recertification intervals may be different and may require additional evidence of continued professional development.
Vision requirements are a mandatory, often overlooked element of NDT certification. Before initial certification and at each recertification, NAS 410 requires that candidates pass a vision examination to confirm near-vision acuity sufficient to read a Jaeger Number 1 (or equivalent, such as 20/25 or better) at a minimum reading distance, with corrective lenses if used. Color vision must also be demonstrated adequate for the specific method—critical for dye penetrant testing, where distinguishing the red indication from the white developer background is a direct safety requirement. These tests must be administered by a qualified examiner and documented.
Why NAS 410 Matters in Practice
For an AMT working in an FAA-certificated repair station or an aviation manufacturing environment, NAS 410 is not merely an academic standard. Part 145 repair station regulations require that personnel performing specialized inspection functions—including NDT—be properly trained and qualified for the work they perform. When the FAA audits a repair station, inspectors will look at personnel qualification records, training documentation, experience logs, and examination results. Gaps in those records can result in findings that ground operations or invalidate completed work.
Beyond regulatory compliance, the tiered qualification framework exists because NDT errors have catastrophic consequences. History records incidents where improperly interpreted NDT results allowed cracked engine disks, corroded spars, and fractured landing gear components to return to service. The three-level structure, the documented experience requirements, and the periodic recertification cycle all exist to prevent those failures.
Key Numbers and Rules
- Three certification levels: Level I (perform under supervision), Level II (perform and evaluate independently), Level III (technical authority and program oversight).
- Three required examinations: General (principles), Specific (employer's procedures and equipment), and Practical (hands-on demonstration).
- Minimum passing score: Defined by the employer's written practice under NAS 410; requirements vary by method and level rather than a single universal percentage.
- Certification period: Maximum interval and interim requirements set by the applicable NAS 410 revision and employer's written practice before recertification is required.
- Vision requirement: Near-vision acuity to read Jaeger Number 1 or equivalent; adequate color vision for the specific method.
- Certifying authority: The employer's Level III or authorized NDT examining body—not a government agency.
- Experience portability: Hours from previous employers are credited if adequately documented.
Common Test Traps
- Confusing who certifies NDT personnel. NAS 410 certification is granted by the employer (through its Level III), not by the FAA or a government body. Students often assume federal oversight is direct when it is actually indirect through repair station regulations.
- Misidentifying Level I authority. Level I technicians can set up equipment and perform tests but cannot independently evaluate or accept/reject indications. Any answer suggesting Level I can make accept/reject decisions is wrong.
- Forgetting vision requirements. The knowledge test frequently tests whether students know that vision—including color vision—must be formally verified before certification. Many students overlook this as a qualification component.
- Assuming all NDT methods have identical hour requirements. Training and experience hours vary by NDT method because of differences in technical complexity. Radiography and ultrasonics require significantly more training than liquid penetrant, for example.
- Overlooking recertification intervals. NAS 410 imposes a maximum certification period defined by the applicable revision and employer's written practice. Failing to recertify means the technician's certification lapses, and previously performed work may be called into question during an audit.