4.3 Practical/Hands-on Oversight, Competency Evaluation & Vision Requirements

Administering the Practical Examination

The practical examination is where a candidate proves competence, not just knowledge. The Level III builds a specimen set whose parts represent realistic materials, geometry, and known discontinuity conditions — that realism is what makes a practical exam strong. The candidate must set up and operate the equipment, calibrate against the correct reference standard, scan or process the specimen, detect the relevant discontinuities, evaluate them against acceptance criteria, and report results in the required format. Because the examiner knows exactly what is in each specimen, scoring can be objective: credit is given for correctly finding and characterizing the known flaws and for correct operations, and points are lost for missed flaws or false calls.

Specimen Sets and Checkpoints

SNT-TC-1A frames the practical around one or more flawed specimens plus a set of operations (checkpoints) the candidate must demonstrate — for example selecting the technique, calibrating, and documenting. The Level III controls these specimens like exam content: they are secured so candidates cannot memorize flaw locations, and their flaw maps are documented so grading is repeatable. A well-designed set spans the discontinuity types and part forms the inspector will actually encounter, so passing the practical predicts field competence rather than skill on a single artifact.

Competency Evaluation and Coaching

Beyond the pass/fail practical, the Level III continuously evaluates competency during on-the-job training. A recurring field problem is that trainees repeatedly call harmless geometric features rejectable indications — for example mistaking a fillet-weld toe or a machining step for a crack. The best corrective action is coached practice with known reference conditions plus review of the applicable acceptance criteria, not simply telling the trainee to be more careful. Documentation of competency — a dated log of tasks, hours, and supervisor verification — is what most directly supports a candidate's claimed OJT and experience during an audit.

Vision Requirements

Personnel qualification is invalid without documented vision capability, because NDT depends on resolving fine visual detail. SNT-TC-1A and CP-189 specify two examinations:

• Near-vision acuity. Natural or corrected near-distance acuity in at least one eye sufficient to read a minimum of Jaeger Number 2 (or an equivalent type and size letter) at not less than 12 inches (30 cm) on a standard Jaeger chart. This confirms the person can resolve fine relevant detail at the working distance used for inspection.
• Color-contrast differentiation. The applicant must demonstrate the ability to distinguish and differentiate contrast among the colors or shades of gray used in the method (for example red penetrant against a white developer, or fluorescent green under UV). The 2020 edition frames this as color contrast rather than full color vision, so a color-deficient person who can still differentiate the relevant contrasts may qualify.

How Often Vision Is Tested

Two cautions the Basic exam probes. First, Jaeger Number 1 is finer (more demanding) than Jaeger Number 2; SNT-TC-1A sets J2 as the baseline, but some employer written practices and standards such as aerospace NAS 410 impose the stricter J1 and may add a far-distance acuity requirement that SNT-TC-1A does not. Always read the invoked document rather than assume the SNT-TC-1A minimum. Second, corrected vision is acceptable — the requirement is met with glasses or contacts — so the record should note whether the test was passed corrected or uncorrected.

Records Tie It Together

A complete certification record must show training, experience, examination results (general, specific, practical), and current vision status. During an audit, the single record that best demonstrates a Level II was certified in accordance with the written practice is a signed certification record showing training, experience, exam results, and vision status. If the near-vision test has lapsed past its annual interval, or the color-contrast test past its five-year interval, the person's certification is not properly maintained regardless of how strong the exam scores were — vision currency is an independent gate, just as the 70% practical floor is an independent gate on the composite grade.

Worked Example: Scoring a Practical

Suppose a penetrant practical uses a specimen set containing eight known surface-breaking discontinuities plus five operational checkpoints (surface preparation, penetrant dwell, emulsification, development, and reporting). The Level III can weight detection and operations together: if the candidate correctly finds seven of eight flaws and performs all five operations correctly, the raw practical score is (7 + 5)/(8 + 5) = 12/13 = 92%. That score then feeds the composite alongside the general and specific grades. A missed flaw and, worse, a false call on a harmless geometric feature both cost points — which is exactly why coached practice on known reference conditions matters before the graded attempt.

Why Color Contrast Is Method-Specific

The color-contrast requirement is not abstract. In visible penetrant testing the inspector must separate red indications from a white developer; in fluorescent methods, green or yellow-green indications must stand out under ultraviolet light in a darkened booth; in radiography the reader distinguishes subtle shades of gray on film or a monitor. A candidate who cannot resolve the specific contrast a method relies on cannot be qualified for that method even when general acuity is fine — this is why the test is tied to the colors or shades of gray actually used.