Considering Human Factors Impact During Aircraft Inspection Tasks

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On July 6, 1996, a McDonnell Douglas MD-88 equipped with Pratt & Whitney JT8D-219 turbofan engines, was on take-off roll from Runway 17 at Pensacola when it experienced an uncontained, catastrophic turbine engine failure that caused debris from the front compressor hub of the number one left engine to penetrate the left aft fuselage. The impact left two passengers dead and two severely injured; the two dead were a mother and son. The pilot aborted take-off and the airplane stopped on the runway.

The NTSB determined the most probable cause of the accident was a fracture in the left engine's front compressor fan hub, which resulted from failure of the airline's fluorescent penetrant inspection process to detect a potentially dangerous crack in the fan which originated from the engine's initial manufacture.

The NTSB also attributed the accident to the failure of Delta's maintenance team to discover the problem.

Inspection reliability must encompass human inspector reliability so that knowledge of human inspection performance is vital to safety. The above tragic accident serves to re-enforce the importance of effective inspection and to never forget lives are dependent on doing our job correctly with knowledge and competence.

Visual Inspection is a Primary Maintenance Activity

Visual Inspection plays a critical role in airworthiness assurance. Used both for finding “failure conditions” and as a validation regarding the effective performance of maintenance tasks as a final check that the maintenance has been performed correctly.

Inspection failure can have consequences and a critical defect may remain undetected.

One area of human activity which needs to be considered concerns the fact that.

as time on the task increases, then the probability of our ability to detect defects decreases.

It is understood that detection performance decreases rapidly over the first 20-30 minutes of an inspection task and remains at a lower level as time or task increases.

Note - performance gradually worsens until it reaches a steady low level.

Vigilance decrements are worse for rare events, for difficult detection tasks, when no feedback of performance.

Considering Potential Interventions

  1. Training in awareness of best practice techniques and time considerations provides for an improved outcome.
  2. Human performance decreases when faced with adverse noise and thermal environments, unfortunately such adverse conditions are common with both base & line environments.
  3. Inspections should takes place within an ideal physical environment and whilst enough light must be available for inspection performance will also depend on the quality of the visual environment than and lighting should be sufficient to maximize the probability of defect detection.
  4. Relationships between the inspector and others may influence inspection performance, if the inspectors' decisions are contradicted by management, then pressure may be felt to change any decision which has been made or even to impact the overall criteria. Such behaviour can affect inspection reliability.
  5. Poor or ineffective handover procedures can become pre-cursors to errors and have been implicated in incident and accident reports. Procedures should be developed to enforce good practices to be followed whenever it is necessary to handover a job.
  6. Inspection demands continuous vigilance, which is a very demanding activity, Plus it is not uncommon to see long hours of overtime worked adding to the pressure. We do not perform well during long hours of work or when sleep patterns are impacted. (Often Inspection is carried out on night shift). Taken together both factors can affect inspection reliability.

Further Guidance

Sofema Aviation Services (SAS) ( and Sofema Online (SOL) provide training for aircraft inspectors delivered as classroom, webinar & online. For Details please email or

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