I definately think that a great deal of experience can be gained in a hangar. I certainly learnt more after a year in a hangar than I did during the previous 3 on the line. I'm now back on the line and feel more confident on the aircraft. You get to learn where all the zones are,where things are and more detail about the aircraft in general.
Having said that, I was in a hangar in the RAF and was treated like a leper - especially as an avionic trade, so much so that that heavily influenced my PVR decision.
I have gained much valuable information in civil aviation hangars, not just about the aircraft but the way they are managed (or not).
The hangar experience has definately helped in a lot of ways, but depending on your status in a hangar will depend on the experience you gain. Some mechs are excluded or simply not interested in the aircraft sytems when it comes to fault finding or functional checks, so eveyones outlook on the subject will obviously differ.
I have worked with people who could embody any mod going, but would have no idea how to apply power to the aircraft in the first place! (no lie), let alone function the newly installed system.
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NO FAULT FOUND