Duplicate Inspections

           Duplicate Inspections are inspections where the task or process is performed by one person, a first check carried out by that person (if qualified to self-certify) or by a supervising certifying engineer, and then independent checks carried out by a second suitably qualified person. Both the first and second checks should be thorough and, in the case of control systems, ensure that they include functional checks for freedom and full range of movement.

It is important to consider 

                    (i) the criticality of the task and consequences of failure,                                                          (ii) the vulnerability of the task to human error (which might be determined by previous incidents, a risk assessment, etc)                          (iii) the presence or absence of other checks (e.g. functional checks). However, one should not assume that just because other checks are present in the procedures or aircraft systems, that they will be effective.                                                                         It is generally better to have several mechanisms for detecting error and not to rely on just one, or to relax checks (e.g. duplicate inspections) on the assumption that a problem will be detected by one of the other error detection mechanism (e.g. preflight checks by pilots).

Tasks which may Warrant Duplicate Inspections

  • Installation, rigging and adjustments of flight controls
  • Installation of aircraft engines, propellers and rotors
  • Overhaul, calibration or rigging of components such as engines, propellers, transmissions and gearboxes

Avoid overuse of duplicate inspections.                           Overuse, combined with inadequate manpower, can result in checks being skimped and reduce the effectiveness of the duplicate inspection as an error capturing mechanism. It is easy to be lulled into a false sense of security simply because DIs have not found a mistake on a particular system or an individual has not previously made an error. 

   In many respects the onus of responsibility for determining what work requires a duplicate inspection rests with the certifying engineer. For aircraft manufactured more recently it has been a requirement that the manufacturer identify vital points in the aircraft and its systems. Such vital points are points or areas in the design where it has not been entirely possible to eliminate through design the possibility of failure by a single item or incorrect assembly.

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