write:This is usually the hard part of any systems investigation as the distribution plumb-ing is frequently destroyed or severely damaged in the accident. It is very hard to put it back

fuses
circuit breakers) or from destroying the airplane (check valves
filters
filter bypass plumbing
emergency reservoirs
emergency pumps
etc.) Check these.E. DIStRIButIon. The system medium (fluid
air
electricity or mechanical force) has to be distributed somehow to where it is needed. This is done through electrical wiring
hydraulic and fuel plumbing
cables
pulleys
bellcranks and so on. This is usually the hard part of any systems investigation as the distribution plumb-ing is frequently destroyed or severely damaged in the accident. It is very hard to put it back together and say with certainty that it either was or was not working. The best approach is to skip this item temporarily and go to the next one.F. APPLICAtIon. At the end of the distribution scheme
the system does something useful for us. Electrical systems operate motors
lights or electronic equipment. Hydraulic systems use actuators to move things. Mechanical sys-tems move things through leverage and force. One useful investigative ap-proach is to verify that something on the application end of the system was working correctly. If you can do this
then you have pretty much validated the distribution scheme for that branch of the system. If
for example
you are trying to locate an electrical problem
knowledge that the aircraft’s navigation lights were seen by witnesses (and therefore working) can save you a lot of hours of messy wiring investigation. A second useful approach is to examine the actuating device for the part of the system you are interested in. If the motor or actuator wasn’t working correctly
then it really doesn’t make any difference whether the distribution plumbing was intact or not.The whole idea of thinking about systems in this way is to focus the inves-tigation on the easy things and avoid
if at all possible
having to reconstruct the system wiring or plumbing.4. ComPonEnt EXAmInAtIon.In any system investigation
you inevitably work your way down to looking at actual system components; motors
actuators
switches
valves and so on. There is pretty good acronym called PIXTOW which can guide you through an orderly examination of almost any component: P Photograph it. Get pictures of what it looked like before you messed with it. I Index it. This applies to components that rotate or slide or have parts that move. Use a scribe to put a mark across two mating surfaces so
no matter what happens next
you can always restore the moving parts to their “as found” position. X X-ray it. Before you take it apart
think about the advantages of industrial x-ray. This is non-destructive and can show you things that you probably won’t see if you do take it apart. If you are dealing with a switch
for ex-ample
the act of opening it is likely to destroy the evidence of whether the contacts were open or closed.Up to this point
you haven’t done anything to the component that would destroy any evidence. From here on
you are likely to change things and you want to be sure that you have done all the non-destruc-tive things first.