A LOW TIME PVT SMA PLT DSNDS INTO SNA CLASS C AIRSPACE PREMATURELY WHEN CLRED OVER TO FUL TWR. PLT DID NOT REALIZE HE WAS PERFORMING AN UNAUTH PENETRATION OF AIRSPACE.

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I WAS ON A NIGHT XCOUNTRY FLT FROM FALLBROOK (L18) TO FULLERTON; (FUL). AFTER TKOF ESTABLISHED CONTACT WITH SOCAL APCH FOR VFR FLT FOLLOWING BECAUSE I WOULD BE PASSING THROUGH THE SANTA ANA CLASS C. I WAS CRUISING AT 4500 FT MSL OVER JOHN WAYNE ARPT WHEN APCH INSTRUCTED ME TO FLY HDG 270 DEGS; SO I DID. A WHILE AFTER I HAD PASSED N OF SNA; THE CTLR TOLD ME THAT THE FREQ CHANGE (TO FUL) WAS APPROVED; AND THAT I SHOULD 'RESUME OWN NAV TO FULLERTON.' I THEN CHANGED COURSE AND BEGAN MY DSCNT; AND CONTACTED FUL; WHICH CLRED ME INTO CLASS D. A SHORT WHILE LATER; THE FULLERTON CTLR CALLED TO ASK ME WHAT SOCAL HAD TOLD ME; SO I TOLD HIM. HE THEN SAID THAT SOCAL HAD CALLED HIM; AND THAT THEY WERE 'PRETTY UPSET' THAT I HAD BEGUN TO DSND. I REALIZED LATER THAT I HAD BEEN IN CLASS C WITHOUT RADIO CONTACT WITH SOCAL; SINCE THEY AUTHORIZED THE FREQ CHANGE. THEY NEVER ONCE TOLD ME TO MAINTAIN ANY SPECIFIC ALT; NOR DID THEY TELL ME TO REMAIN CLR OF CLASS C. BUT NOW I SEE THAT EVEN IF THE CTLR DISCONTINUES RADIO CONTACT; IT IS STILL MY RESPONSIBILITY TO REMAIN CLR OF CLASS C; DESPITE THE IMPLIED PERMISSION TO CROSS IT DURING MY DSCNT TO THE DEST. HOWEVER; I KNOW THIS SIT COULD HAVE BEEN AVOIDED IF THE CTLR HAD MERELY ADVISED ME TO 'REMAIN ABOVE CLASS C' OR 'MAINTAIN PRESENT ALT.' I WILL BE MORE CAREFUL TO ASK FOR EXPLICIT PERMISSION TO CROSS CLASS C AIRSPACE IN THE FUTURE.