Kingfish wrote:
IIRC flying IFR into an uncontrolled field is a one-in & one-out deal.

Is the one-in, one-out deal a function of having a tower, or of radar
coverage? HPN becomes uncontrolled when the tower closes at 10:00 PM,
but there's radar coverage right down to the ground (NY Approach has a
radar sensor on the field). Does HPN become one-in, one-out when the
tower closes? I come in late at night once in a while, but not often
enough to notice how the IFR works.

In essence you "own" the airspace (not the runway) until you've landed
& cancelled with ATC or flown somewhere else.

The landing has nothing to do with it. The essential event is
cancelling IFR. You can cancel before you land, which releases the
airspace. On the other hand, if you land and don't cancel, ATC will
continue to protect the airspace until you do cancel (although, I
imagine there must be some timeout).

I had an experience a few years back on an IFR training flight into
BDR (Bridgeport, CT). We were holding at the FAF and I could see the
aircraft in front of us (a commuter flight) had already landed and
taxied off the runway. But they hadn't canceled yet, so ATC couldn't
clear us for the approach yet. It worked out fine, since my student
needed the holding practice :-)

Only then can ATC bring in another aircraft for an approach
(assuming IMC conditions exist).

IMC has nothing to do with it. In the BDR example above, it was
severe clear, but if we wanted an approach clearance, we had to wait
until the airspace was released by the flight in front of us
cancelling.