The FIM for any defect usually starts with - check pin 12 for 28v trying to escape or suchlike - but what happens - all these checks are dismissed when the next step is - replace the servo valve, we've got a valve but we haven't got an AVO (or someboby who knows how to turn it on), so the servo valve gets changed. Surprise, surprise it didn't fix it, ADD time, next guy comes along and assumes check pin 12 for 28v trying to escape was done that's why they changed the servo valve. He goes to next step and changes servo valve contoller, thats 2 bits back to the workshops when all along those 28v were never going to escape, well not at pin 12 anyway. Broken wire, bent pin whatever?
We are all to blame, if I had a £5 note for every avionic guy who swore blind the servo valve or controller was faulty rather than go and do the basic wiring checks in the first place I'd have about £500 by now. I'd have more if I hadn't learn't how to use the AVO myself and check for 28v at pin 12.
The good avionic engineer can save a fortune, unfortunately so many have chosen to live in the comfort zone that there effectivity is called into question.
The 777 MAT is great at giving a choice of expensive black boxes to change, when they've all been changed they call in the half decent avionic guy over from the hangar and he finds out the 28v isn't there at pin 12. That's progress for you!
If you are a bean counter I don't suppose you read this stuff any more than you listen to professional engineers.
There is an up side though, bean counters get charged lots of cash for servicing their BMW's, components changed for no good reason other than making a quick profit. What goes around comes around!
[This message has been edited by time-ex (edited 17 March 2001).]