"Peter Bauer" wrote in message
om...

.. when flying under a flight plan (IFR) can i fly routes at my choice ?
e.g. take-off under IMC, enroute 10 min under IFR (clouds), 30 min VFR
on
top, descending to my destination under IMC (through cloúds),
landing
at destination under VMC (below the lower layer of clouds)

.. when reaching IMC after 30 min. VMC ("round trip under VFR") do i have
to file a flight plan (IFR) or am i able to fly only by reference to
the
instruments through an e.g. 300 ft Layer of clouds and after that,
when
reaching "On Top" fly again under VFR ?

You do not say where you are flying, Peter. Others have answered on the
assumption that you are flying in the US, I'll give you an answer for
Germany.

The airspace system in Germany is not very different to that in the US, but
there are a couple of differences. Controlled airspace generally starts at
2500 ft agl rather than 1200 ft agl. Flying under IFR in class G is
forbidden in Germany. Thus for an IFR flight, if your destination is not an
IFR airport surrounded by controlled (or class F) airspace, you usually need
to be able to cancel IFR by the minimum instrument altitude which is not
below 2500 ft. This makes IFR flights to VFR airports fairly painful.

To fly under IFR you need a clearance. Pop-up IFR clearances (if you find
IMC on a VFR flight like your second scenario) are troublesome. I've had to
dictate an entire flight plan (including the colour of the dinghy cover) to
a FIS controller to get an IFR pop-up, despite having filed a VFR plan with
almost exactly the same info.

"VFR on top" clearances, as Pete described are not used in Germany (in fact
they're not used outside the US). But you will find that practical IFR
clearances tend to include long direct legs, so it's unusual to be in a
situation where a VFR routing will save you a lot over an IFR one.

So where are you based?

Hope that helps

Julian Scarfe