Big John wrote in message
It's interesting that you point out how one can legally fly without a
medical certificate. Haven't seen it talked about for years.

I did look up the class-III thing quite a while ago and made sure I
understood it properly because i) I wanted to become a CFI (still not
there yet, I should stop procrastinating and take the exam ...:-);
and ii) only had a class-III at the time with a SODA limited to class-III
only and I wasn't sure whether I could upgrade it to class-II or higher;
turned out that I was able to do so (all it took was additional time to
process the paper work and another medical flight test, no biggie; but
I digress; anyway, the point is that when you have to get SODA to fly,
you end up having to learn the regs pretty well :-)

except that I made a mistake (hope you guys would have corrected it,
but just to be sure):

(which is why one can be paid as a flight instructor
with just a class-III medical certificate or even without any valid
medical certificate if one is acting as PIC, or as required crew member,
see 61.23(b)(5)); i.e., while instructing, a CFI is only exercising
the privileges of a private pilot...

I meant to say: if one is NOT acting as PIC or as required crew member...

for instance, when you are teaching an advanced student (already rated
in category and class -- and type as the case may be -- and with proper
endorsement should it be a complex/high-perf/tailwheel) who can act as
PIC...

--Sylvain