[cz_raf]

Chris and Nick thank you both for your comments and suggestions.
I agree with Chris that those possibilities offered by Nick does not seems to be the case I am after.
Chris is also right that there were mostly only radar contacts and then once sighting on long distance so no identification was possible.
From the long presence, low height and possibly circling I would guess they were searching for something...
Well seems to me as another mystery hard to solve.



Pavel