I need to improve the DOC of the Fokker F27 specifically in terms of the avionics and control system (if applicable). Searching google for an exact definition of aircraft DOC is proving a bit difficult as most sites just give some formula to calculate it but don't really mention anything specifically in terms of time-scales involved.
You appear to be considering operating costs purely in terms of maintenance cost, whereas that only accounts for a proportion of DOCs.
A good start might be to establish, for typical F-27 operators, what proportion of DOCs is actually represented by maintenance. That will then give you a better idea of the maximum savings that maintainability improvements would produce, which you can then compare with the cost of any such changes.