I operate a Bombardier Dash 8 Q400. I want to know if aircraft engineers are mandated to close or rectify a defect by only following the fault isolation manual (FIM). Can an engineer instead use his knowledge and experience of the systems to isolate the problem and resolve the defect?
FIM contains procedures for both A/C systems (E.G. EICAS, ECAM, CPDS) messages and pilots/maitenance observations (e.g. smell of burning oil, windshield delamination). All kind of reasonably possible faults should be covered by FIM.
Just simply use yor FIM preambule to determine if it specifies what to do when fault is not covered by FIM and to determine either mechanic judgement or OEM (A/C manufacturer)contact is requied in such case. If such information is not included contact OEM.