All what has been said so far is correct. I will add another couple of things. Firstly BIT. BIT is only as good as the sytem requirements.
I am an Ex RAF Comms Technician so fit into the older technician bracket, so have some knowledge.
However, as part of the team working on the EFA DASS. We were not allowed to expand the range of BIT outside what was required/mandated by the requirements despite the fact that I knew what it did not cover. So BIT is a useful tool but it will not point you in the correct direction all the time hence where system wide knowledge and not only sub system knowledge is useful.
One thing which can reduce the amount of technical support is good logistics back up. Having spares redilly available is helpful beyond measure. The amount of time taken to Rob spares and do the paperwork is unbelievable. With good spares back up and instantly available, aaahhhhhh luxury.