PLT OF A PIPER PA34-200 MAY HAVE INADVERTENTLY PENETRATED CLASS B AIRSPACE DURING A VISUAL DSCNT TO AN UNDERLYING ARPT CAUSED WHEN THE PNF CANCELED THEIR IFR CLRNC. THE RPTING PLT DISCOVERED HIS MISTAKE AND MADE A RAPID DSCNT TO AVOID OR GET OUT OF THE CLASS B AIRSPACE.

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THE IFR FLT WAS NEARING THE END OF ITS JOURNEY FROM ASPEN TO SAN CARLOS (SQL). THE FLT HAD GONE WELL AND ABOUT 4 HRS HAD ELAPSED. THE WX WAS GOOD; AND THE CREW (PF AND PNF) HAD FLOWN MANY TIMES TOGETHER USING CRM. PRIOR TO REACHING SUNOL INTXN; THE FLT WAS VECTORED FOR A VISUAL APCH. WE RECEIVED A VERY EARLY HDOF TO SAN CARLOS; PERHAPS 20 MI OUT. THIS WAS WELL BEFORE REACHING THE CLASS B/C COMPLEX IN THE SAN FRANCISCO BAY AREA. THE FLT HAD BEEN HIGH; USING A SLOW DSCNT RATE (300-500 FPM) TO PRACTICE DSCNT PLANNING; CAPITALIZE ON THE SPD GAINED IN THE DSCNT; AND MAKE IT COMFORTABLE FOR THE PAX. NO CONSIDERATION HAD BEEN GIVEN BY THE PF (ME) TO CLASS B/C AVOIDANCE BECAUSE WE WERE IFR. UPON ESTABLISHING CONTACT WITH SAN CARLOS TWR; THE PNF ACCEPTED THE SUGGESTION TO CANCEL IFR. THIS MAY HAVE ARISEN DUE TO THE VFR STYLE OF INITIATING CONTACT BY THE PNF (IE; 'OVER COYOTE HILLS; FOR LNDG WITH CURRENT ATIS' VERSUS 'WITH YOU ON THE VISUAL APCH'). THE FLT WAS DSNDING THROUGH APPROX 3000 FT AT THAT TIME. THE PNF CANCELED IFR; BUT AT THAT POINT WE WERE ABOUT TO PENETRATE THE CLASS B AND/OR OAKLAND CLASS C AIRSPACE; BUT IT DID NOT REALLY REGISTER WITH EITHER PLT AT THAT TIME. I SAW OUR POS ON THE GPS-DRIVEN ARGUS MAP; AND SUDDENLY REALIZED WE WERE ABOUT TO PENETRATE THE CLASS B/C AIRSPACE; AND WE DID NOT HAVE A CLRNC NOR WERE WE IN COM WITH BAY OR OAK TWR. I INITIATED A RAPID DSCNT (APPROX 2000 FPM) TO AVOID AND/OR EXIT THE CLASS B/C AIRSPACE. I DO NOT REALLY KNOW IF A VIOLATION OCCURRED OR NOT. HOWEVER; WHETHER AN AIRSPACE VIOLATION OCCURRED OR NOT; I BELIEVE AN UNSAFE CONDITION EXISTED BY VIRTUE OF A SUDDEN; RAPID DSCNT AT LOW ALT AT THE EDGE OF BUSY AIRSPACE. WHILE I AM NOT AWARE OF ANY OTHER AIRPLANES IN THE VICINITY AT THE TIME; I MUST CONFESS I DID NOT LOOK FOR THEM PRIOR TO DSNDING; EITHER. THE AIRSPACE ISSUE TOOK PRECEDENCE IN MY THINKING OVER POSSIBLE COLLISION AVOIDANCE. IN MY VIEW; THE CONTRIBUTING FACTORS WERE: FATIGUE -- AFTER 4 HRS IN THE AIR; NEITHER PLT COMPREHENDED THE IMPLICATIONS OF SWITCHING FROM IFR TO VFR AT THAT POINT IN SPACE. NONSTANDARD PROCS -- BAY HANDED THE FLT OFF TO SQL MUCH EARLIER THAN USUAL. (A NORMAL HDOF WOULD HAVE OCCURRED IN SUCH A WAY THAT WE WOULD HAVE ALREADY BEEN IN THE CLASS B/C AIRSPACE WHEN HANDED OVER TO SQL TWR). ALSO; THE PNF USED NONSTANDARD PHRASEOLOGY WHEN CONTACTING THE TWR. LACK OF CREW COORD - - THE PNF SHOULD HAVE ASKED THE PF PRIOR TO CANCELING IFR.