Functional Checks

           Functional checks are error capturing mechanisms in some instances since they will detect, if properly actioned, if something is not installed, secured properly, adjusted correctly or meets specified criteria in the manuals. This is true for most systems and is an inherent part of the maintenance process.          It is, in the majority of cases, impossible to carry out a duplicate inspection on a flying control without a function check since the range of movement, control stop clearances, control system friction or loading checks cannot be determined otherwise. 

               The problem is that since they are regarded as an inherent part of the system, complacency can set in concerning their purpose and value. It is only when the function checks or ground runs are not carried out and an incident occurs, (e.g.  double engine oil loss on a 737-400 at Daventry) that their benefit in error prevention or error capture is properly realised. 

       It is important to carry out the functional check carefully, and to observe and note the consequences.                                                            There have been several instances where the actions of a check procedure have been carried out but not the observations.                        It is also important to carry out the check correctly. An incident occurred were the left hand stick in an aircraft functioned incorrectly due to a cross-connection error during maintenance. However, the functional check was carried out on the right hand stick, therefore failed to detect the problem, 

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