I was a troubleshooting specialist for a major airline for my last 15 years of employment. As such, I decided to analyze the profession and determine what it really takes to be a good troubleshooter. We've all heard of 5 or 7 or ? point troubleshooting guides, but the complexity of troubleshooting can never be covered by such simplistic guides. So I ask you is there one absolutely necessary piece of knowledge for all troubleshooting? The answer is yes and only one. Troubleshooting is accomplished by making tests. Those tests may be moving the flap handle and watching an indicator's response, or a VHF NAV ramp test, or simply placing the probes of a multimeter on test points.
Well, most A&P's can do those things so where is the rub? Its not making the test, its knowing the correct value or indication before making the test. If you place the flap handle at 15 degrees and watch a corresponding indicator and do not know how that indicator should respond, you have only introduced confusion into the process. If you measure 28 VDC at a relay contact and don't know if that is a correct voltage for the present aircraft configuration, you have only introduced more confusion into the process.
How can we know the correct value or indication? Training? Not hardly. Very seldom do training classes get down to the nitty gritty details of voltages at every test point for every configuration. Even if they did, you would not be able to remember such abstract information. In short, you have to figure it out.
When I was assigned to lead a troubleshooting effort, the first thing I did was to pull all the applicable schematics, sit down at a table, and begin marking them up with colored pencils. Why? It provided me with a comparison model that indicated the correct voltage at every test point for the configuration of the airplane at the point of failure. With that data in hand, I could properly evaluate every test necessary to isolate the fault.
There's a great deal more to troubleshooting, but that's for a later post.
