(Bravo8500) wrote:
In a recent FAA sponsored seminar that I attended, a retired Tower
Controller mentioned in his presentation that IMC flight in Class G
airspace without a clearance was actually legal as long as the
aircraft and pilot were both instrument qualified.

That's correct.

After I got home
that afternoon, I thought to myself that if that were the case, then
when I'm at MDA on my local uncontrolled airport's NDB approach, and I
don't see the runway but can see directly underneath me, I could
legally slip down below MDA to try to bust out.

Nope. The one and only difference between IFR flight in controlled and
uncontrolled airspace is that in uncontrolled (i.e. Class G) airspace,
you won't have an ATC clearance (i.e. 91.173 does not apply). All this
means is that ATC is not providing you with separation services. You
are still IFR, and everything else related to IFR still applies.

91.175 says you have to obey MDA's while making an instrument approach
in instrument conditions. 91.177 says you have to obey minimum
altitudes prescribed in part 97 (which in turn includes all the
published SIAPs by reference). There is nothing in either of those two
sections which says they don't apply in CGAS.