I echo AAs yes yes and yes.
You don’t need a clearance into the next CAS entry because you are already cleared to your destination 99.9% of the time. You will be handed off to the next ATC in the case of CAS/CAS or to the FIS (Sweden Control) if CAS/OCAS, and then again from FIS/ATC as you approach a CAS boundary. But the new ATC doesn’t reclear you into CAS because that is already assumed (although they might give you an amended clearance).
“you don’t get RT reply in RMZ OCAS while IFR, do you become a VFR ?”
I don’t know what you mean. No you don’t become VFR unless you can remain VMC and you cancel IFR. If you don’t get a reply you apply lost comms procedures.
Ibra wrote:
For CAS acess/handover: do you get explicit clearance for next CAS entry or handover contact to the next sector? or you are always talking to same ATC with a FIS hat while you are OCAS?
You get a route clearance to destination on departure. (Even if your departure airport doesn’t have ATS, you’ll get a route clearance on first contact with ATC/FIS.)
So you don’t get (or need) any additional clearance when (re)entering CAS or on handover.
When you are flying OCAS, FIS is generally provided (both for IFR or VFR) by the controller for the nearest ATC sector above. Near uncontrolled instrument airports, FIS would instead be provided by the AFIS unit of the airport. Apart from that Sweden doesn’t have specific FIS sectors. (Unlike e.g. Germany.) There are both advantages and disadvantages with this system.
Not sure if this is ever the case for Sweden airspace but let’s assume it’s 2 different CAS ATC & 3rd different FIS OCAS in the middle, you don’t get RT reply in RMZ OCAS while IFR, do you become a VFR ?
That airspace configuration could happen in principle, but I don’t know if it actually does. If you don’t get RT replies in a RMZ OCAS then it is a comfailure situation. If that happened to me, I would do the same as with any handover – return to the previous frequency and report unable to contact. It will never happen that you are silently “dropped” or “become VFR.”
Ibra wrote:
For CAS acess/handover: do you get explicit clearance for next CAS entry or handover contact to the next sector? or you are always talking to same ATC with a FIS hat while you are OCAS?
One more comment on this: It is usually transparent whether (when IFR) you fly in controlled or uncontrolled airspace. That is both a good and a bad thing… When leaving CAS the only difference compared to a CAS/CAS handover is that you are told (usually) “no reported traffic in uncontrolled airspace”.
I can also add that Swedish ATC can’t clear you out of CAS unless it is clear (by flight plan or request) that’s what you want.
Taking this back to the UK 
this dodgy practice is partly a consequence of most CAS+OCAS routes validating via Eurocontrol.
The UK could have chosen to supply Eurocontrol with standard routes and banned all other routes. One way is to set MAXDCT=0 and then only published airways will route, and you can put in the MEA as a constraint. I recall Albania’s airspace is like that. It also means any airport to which you want to fly IFR must have SIDs and STARs published. It would also make it almost impossible to do “GA IFR” in the UK because you would have to fly in narrow corridors, and often FL150+ This is an old map but is very close
But ultimately the disconnect in ATC service is due to ATC funding and the politics related to that… I think there are some serious rivalries between different units / different companies. For example Solent quite clearly doesn’t like talking to Bournemouth even though their CAS is joined up! And why doesn’t Solent or Bournemouth link up with Exeter, using this
or even, keeping it in line with ATC technology, with this
And why does the UK system (not sure who runs this bit) toss flight plans they receive from Eurocontrol in the dustbin if they are “too low”? And if they don’t toss them in the bin immediately, why do they toss them in the bin as soon as you have exited the first bit of CAS?
Cttime wrote:
“you don’t get RT reply in RMZ OCAS while IFR, do you become a VFR ?”
I don’t know what you mean. No you don’t become VFR unless you can remain VMC and you cancel IFR. If you don’t get a reply you apply lost comms procedures.
Airborne_Again wrote:
If you don’t get RT replies in a RMZ OCAS then it is a comfailure situation
Got it, I guess talking to Sweden FIS (Sweden Control, is radar unit?) keeps the show going or at least you are expected on both sides
Same as talking to FIS with radar (Scottish Info or ATC radar units Luton/Essex/Thames doing FIS deconfliction) does keep the show going
Talking to London Info (FIS with no radar) between ATC units is where “lost in translation” ICAO procedure applies 
If you get “freecall en-route” it’s done !
Ibra wrote:
Sweden FIS (Sweden Control, is radar unit?)
Yes, but it does not necessarily have radar coverage in all of uncontrolled airspace.
Ibra wrote:
If you get “freecall en-route” it’s done !
Unable, my IFR chart doesn’t depict all airspace.
Airborne_Again wrote:
No. You still need to follow the rules. E.g. if a controller clears you at 500 ft over at town, you will bust the minimum height ruls. If the controller clears you VFR at 2500’ and the cloudbase is 2600’ you will bust the distance from cloud rule. In both these cases you must say that you are unable to accept the clearance and request a revised one. It would be the same thing if the controller clears you into class A on a VFR flight.
I have had and followed various instructions from French ATC which break other rules – usually to do with flying lower than usually allowed or being asked to fly into a prohibited zone or class A VFR. The two I remember off the top of my head are:
1.Summer 2018 flying along the coastal route around Nice/Monaco, the 500ft part. I descended to 500ft on the QNH given and the controller almost immediately requested I descend a further 200ft. I remember confirming my height and the QNH setting and asked for confirmation, which they gave saying there was commercial traffic inbound.
2. A few years ago there was low level haze with poor viz leaving St Cyr L’ecole and on contacting Paris Info they immediately cleared me to climb into the Class A VFR. I repeated I was VFR when responding and they confirmed I should climb to 2500ft above the crud.
Regards, SD..
Dimme wrote:
Unable, my IFR chart doesn’t depict all airspace
Indeed if you treat no “handover frequency” as IFR lost com you are off the hook
Will try one day but I need to hold a non-UK PPL
Can’t speak for IFR, unfortunately, yet, but in case of VFR in Poland I often go OCAS → CAS → OCAS → CAS and get cleared into each bit of CAS (usually a TMA, but also CTR and others) independently, but without any delay or discussion; FIS usually arranges the handoff and all I do is call the appropriate controller. One could just treat G as controlled airspace.
If the CAS → OCAS → CAS is during descent (eg. clipping the layers of a TMA) I usually only get cleared for the 1st one, but this case stays with the same ATC unit.
