Inspecting in the Dark and the Noise
An inspector is asked to examine the composite wing leading edge of a regional turboprop for lightning-strike damage after a reported strike. The hangar bay has general lighting of about 300 lux; a portable lamp is available but its cable is taped across the floor and the lamp flickers. An APU on the adjacent aircraft is running at about 95 dB(A) and the inspector is wearing no hearing protection. He spends 12 minutes on the inspection, finds two small marks, and signs it off. Three days later, a 40 mm delamination is found during a borescope inspection.
1. Which physical environment factors may have affected the inspector's performance, and how?
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- Illumination: about 300 lux is low for detailed composite inspection, where surface gloss changes, shadow lines and small delaminations must be detected. Low light reduces contrast and visual acuity and increases time needed per unit area. The flickering portable lamp adds a stroboscopic effect that can mask small defects and cause eye strain.
- Noise: about 95 dB(A) from the adjacent APU is fatiguing, interferes with concentration and makes verbal cross-checking difficult. Without hearing protection, the inspector also faces longer-term hearing damage and additional fatigue.
- Access and layout: the taped cable is a trip hazard and discourages moving the lamp to different angles, so parts of the surface may be inspected from one poor angle only.
- Time/task design: 12 minutes is short for a full leading-edge scan; inspection is a vigilance task where performance falls off quickly without breaks or a defined scan pattern.
These factors combine: poor light and flicker reduce the probability of detecting a low-contrast defect, while noise and time pressure reduce the attention available to compensate.
2. What controls should have been in place before the inspection started, and who is responsible for them?
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Controls:
- Adequate task lighting – local, steady, adjustable lighting positioned to give raking light across the composite surface; the flickering lamp should be replaced, not used.
- Noise control – schedule the APU run outside the inspection, or move the aircraft, or provide hearing protection and accept a defined exposure limit.
- Safe cable management – route cables overhead or use cordless lamps so the inspector can move freely around the surface.
- Defined inspection method – a written scan pattern, reference standards, allowed defect sizes, and a maximum continuous inspection time with breaks.
- Competence and equipment check – confirm the inspector has composite inspection training and any required aids (tap test, borescope, magnifier).
Responsibility is shared. The supervisor/planner is responsible for the environment and scheduling; the inspector is responsible for refusing to start or continue when lighting or noise is clearly inadequate and for raising it. The organisation is responsible for providing standards, equipment and a reporting route that does not penalise stopping the task.
3. Would you attribute the missed delamination to the inspector alone? Justify your answer and state what should be reported.
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No. Attributing it to the inspector alone would be an individual-blame conclusion that ignores the conditions he was working under. The missed 40 mm delamination is consistent with the combination of low illumination, flickering local light, high noise, short inspection time and constrained access. A competent inspector under those conditions can still miss a low-contrast defect; the environment degraded the signal below the detection threshold.
That does not remove individual responsibility entirely: if the lighting was visibly inadequate, the inspector should have stopped and reported it. But the dominant causes are systemic.
What should be reported:
- An occurrence/near-miss report describing the missed delamination and the conditions of inspection.
- The lighting and noise measurements, the lamp condition, and the inspection duration.
- A review of composite inspection standards, equipment and scheduling for that bay.
- Consideration of a re-inspection of other aircraft inspected in the same bay under the same conditions.
The reasoning is that the report must capture the environment as well as the person, so the corrective action fixes the conditions rather than only the individual.