"O. Sami Saydjari" wrote
OK. It just happened, in this case, that ATC was able to let us go down
to what was coincidentally that MSA for the area.

Right. The operational altitude is really MVA, which is not available
to you. It could be a lot lower. Right off, I can think of some
airports where it is 1400 ft lower, because the obstructions that
drive the MSA are over 20 miles from the airport.

So, my question becomes, at what point do you abort the attempt to go
visual and transition to an IFR approach.

That's your decision as PIC.

Say, you have a GPS and ATC
cleared you down to 2000 ft AGL and you are 10 miles from the airport.
Do you continue at that altitude to the airport until you are right on
top of it (controller permitting), notice that you are still not out of
the clouds, and then ask for an IFR approach at that point?

You could do that. Sometimes it even works. Cloud bases are often
ragged. Or you could tell him that you're still in solid IMC and need
the approach. Your call.

Just trying
to see how the transition from "going for visual" to "err, no can
do...need an instrument" happens. Does the controller force the
decision at some distance out?

That all depends on the MVA boundaries, traffic, etc. For example,
I'm familiar with one field where the MVA is 1700 MSL from one
direction, 2000 from another, and the dividing line seems to be about
a mile from the field. As a result, if you approach from the right
direction, you can get a descent to 1700 - but if you don't get the
airport in sight in a timely manner, you get a climb which essentially
destroys any chance of doing the visual.

In general, the controller will prefer you do the visual if he has a
preference at all - it's less work than vectoring you to final, ties
up less airspace, gets you out of his hair quicker, etc. The only
time a controller doesn't want you to do the visual is if he thinks
you won't get in.

Michael