You can switch back and forth between IFR and VFR if you want but you may it
inconvenient, since every time you want to go back to IFR, you need to
obtain the necessary clearance from ATC (assuming not in Class G
airspace...in controlled airspace, you must have an ATC clearance and an IFR
flight plan in order to fly in IMC, even briefly). There is a way to file a
mixed IFR/VFR flight plan, but I've never heard of that being used when you
need IFR at both the departure and arrival ends of the flight.


But what ...when descending under VMC into Class G Airspace and then
coming into IMC "wheather" (e.g. fog,..) then i can fly IFR without a
clearance ???
If a second pilot does the same "plan" .... very dangerous, isn't it ?
Nobody knows from each other flying in fog...


Typically, if you're flying under IFR, find yourself in VMC and want to take
advantage of that to operate under the flexibility of VFR, you'd get a "VFR
on top" clearance. That's an IFR clearance, and you would still be
operating under IFR, but you usually would get the flexibility of choosing
your routing and altitude as if you were VFR (and in fact would have to fly
the +500' VFR cruising altitudes rather than the even thousands IFR cruising
altitudes).

i can really fly VFR under an IFR-Flight Plan ??
But probably with the same "squawk" as under IFR ?
...and then after getting "tired" flying VFR ..changing back to the
initial IFR Flight Plan ? (what is when too far away under VFR flying
from the "filed" Plan ???
Does ATC give me then another "Plan", an "abbreviated" Flight Plan ?



For example, taking your first scenario, done this way, you'd take off in
IMC, arrive at VMC above the clouds, get a "VFR on top" clearance, fly in
VMC using VFR altitudes and procedures for 30 minutes, and then descend back
to your destination through IMC for the landing, possibly flying a full
instrument approach.

Your flight plan would be for the entire flight, you'd be flying under IFR
for the entire flight, but the time during which you were flying with a "VFR
on top" clearance, you'd be able to get most of the advantage you'd get had
you cancelled IFR and flown VFR for that period.

Something to keep in mind that some new instrument pilots forget: "VFR on
top" does not require that there be IMC below you. It can be used any time
you can maintain VMC. If you're cruising along IFR, but there's not a cloud
for 100 miles and ATC starts vectoring you around or slowing you down or
gives you a hold, often you can use the "VFR on top" clearance to resolve
whatever issue ATC had, and allow yourself to proceed directly to whereever
you were headed.


Well, i haven't known about this......because i'm only an PP-ASEL
without
IFR-Privileges. But the described possibilitites makes it very
interesting getting an IFR-Pilot ;-)



Basically, when IFR procedures become inconvenient and VMC prevails, "VFR on
top" allows you to practically fly VFR without giving up your IFR clearance.

Pete


Thanks to you...Pete


Peter