My tips for a successful CAS transit are....
- Avoid the approach and departure ends of the runway and if possible ask for overhead at 90 deg to the runway. Maybe have a look at the instrument charts to see where IFR traffic is likely to be and avoid.
- State your route explicitly i.e. "request zone transit from <vrp> to <vrp> via the overhead". Or "request zone transit from SAM25 to NEDUL via BIA"
- If they refuse come back with "will accept alternate routing"
- Be sharp and don't stutter or "err err err"...
Example:
"Bournemouth Radar GABCD request zone transit"
"GABCD pass your message"
"GABCD, Rockwell Commander 112, from Bristol to Jersey IFR, 10 miles north of Bournemoth, 3000, request zone transit from SAM25 to NEDUL via BIA"
or
"Bournemouth radar, GABCD request zone transit"
"GABCD pass your message"
"GABCD, Rockwell Commander 112, from Bristol to Jersey VFR, 10 miles north of Bournemouth, 3000, request zone transit from Tarrant Rushton to Hengistbury Head via the overhead"
This is probably not strictly according to CAP124blah as I can't be bothered to state headings, pressures blah blah, but it has never failed to work (who you are, what you are and what you want).
In the second example you would get a squawk, a "not above" and probably a "report" something - like report overhead along with traffic info.
In the first you'd probably get a squawk, an altitude and when you enter the zone a "radar control service". If they vector you, just follow the vectors, but otherwise just follow your requested or cleared route. If you are limited in alt due to an IMC rating I'd ask for a "zone transit IFR at 3000" or whatever.
I'm always happy to fly with people who want to go and do stuff like this and do the radio work. One of my buddies is fairly low houred and we go off on "difficult" flights deliberately to increase his experience. With two onboard it is a great way to do it safely without busting any airspace.....
I suppose these days with AFPEx one can address the flight plan to whoever, and when I go to the channel Islands I always address it to Bournemouth and Southampton. DOn't know if it makes any difference, but I suppose you could file an IFR routing which crosses their airspace and so they are aware of you before you arrive?????