Originally Posted by
Highland Director
Some pilots take a more bold approach. i.e. '<callsign> cancelling IFR flight plan, leaving FLXX VFR. Again, I'd respond with the standard acknowledgement and immediately treat the flight as VFR.
Clearances are not mandatory for flights outside controlled airspace (and outside ATZs).
'<callsign> procedural separation service declined, leaving FLXX IFR'
is even bolder, but in principle is perfectly legal.
It makes good sense to coordinate any impending plan with ATC, whether in VMC or IMC. Thus a "request", or at least an opportunity for ATC to say "I wouldn't do that if I were you because...", is preferable.