Avoiding and Capturing Errors

           Whilst the system should aim for error avoidance, it is not always possible to prevent errors from happening, in which case, the next best thing is to detect them and prevent them from resulting in harm.                                                    The only sure way to be totally safe in aviation is to keep aircraft on the ground, but this is only an option in very extreme cases.        In normal operations, circumstances known to be vulnerable to error can often be avoided, or additional checks put in place to capture errors if they do occur.                                                     One example is work carried out when maintenance personnel are likely to be less alert, where the risks can be reduced if safety critical tasks are rescheduled for other times.       Another example is where warnings can be printed on workcards where there have been previous incidents involving a particular task or procedure.                                                                   It is particularly important to learn (from your quality system, MEMS, or feedback from human factors training, etc) which situations are particularly vulnerable to error, and to implement measures to guard against error in these areas.                                                                             Error capturing forms an important part of the safety net.                                                   There are many types of error capturing mechanisms, including functional checks, leak checks, inspection of tasks before signing for work done by others, independent Duplicate Inspections (DIs), pilot pre-flight checks, etc. AMC-145.A.65(b) highlights tasks particularly vulnerable to error, where special attention should be given to error capturing mechanisms.                                                                         It does not specify what those mechanisms should be, and different countries and companies have their own preferred methods, e.g. duplicate inspections are used by many companies as an error checking mechanism with respect to safety critical tasks.                                                                     Another mechanism, not so much for capturing error, but more to prevent repeated errors from having catastrophic failures, is that of disturbing only half the systems on an aircraft at any one time, where safety critical systems are involved.                                                      For instance, ETOPS principles stagger work on engines such that a similar error (e.g. failing to close oil filler caps) would not occur on both engines at once.                                              Maintenance staff should be made aware in their human factors training that there are very good reasons for procedures such as these, and the importance of applying such error capturing and prevention mechanisms in maintenance. 

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