A PVT C500 FLC DSNDS THROUGH CLASS B AIRSPACE WITHOUT AUTH WHEN THEY HAVE A MISCOM WITH A CTR CTLR CONCERNING THEIR VFR DSCNT.

Narrative

OUR ACFT WAS ON AN IFR FLT PLAN FROM LGA TO DPA. WHILE ENRTE TO DPA; ZAU HAD US START OUR DSCNT. ONCE OUR ACFT WAS BELOW FL180; WE CANCELED IFR AND ADVISED ZAU WE WOULD PROCEED VFR TO DUPAGE ARPT AT 16500 FT. ZAU HAD US MAINTAIN OUR SQUAWK FOR VFR ADVISORIES. WE ADVISED CTR WE WOULD BE DIRECT DPA AT 16500 FT AND ONCE CLR OF CLASS B AIRSPACE WOULD DSND BELOW CLASS B AND TURN BACK TO DPA WHICH IS BELOW CLASS B AIRSPACE. AS WE CONTINUED TO DPA; CTR GAVE US MANY FREQ CHANGES FOR CONTINUED FLT FOLLOWING. WE ADVISED THE NEW CTLRS OF OUR INTENTIONS OF REMAINING CLR OF CLASS B AIRSPACE. OUR ACFT WAS APPROX 15 MI E OF DUPAGE ARPT WHEN THE CTLR ADVISED US THAT ALL TFC IN OUR AREA WAS CLR OF US. THE CTLR SPECIFICALLY STATED 'TFC WAS BEHIND US' AND THAT WE COULD DSND CLRLY TO THE DUPAGE ARPT. I ASKED THE CAPT TO GET A STATEMENT FROM THE CTLR SAYING WE WERE CLRED THROUGH CLASS B AIRSPACE. THE CAPT ASKED THE CTLR IF WE WERE CLRED THROUGH CLASS B AIRSPACE. THE CTLR REPLIED BY SAYING THE AREA WAS CLR OF TFC AND NOW WOULD BE A GOOD TIME TO DSND. THE CAPT SAID 'OK; WE WILL LEAVE 16500 FT; DSND THROUGH CLASS B STRAIGHT TO DUPAGE.' AT NO TIME DID THE CTLR INDICATE THAT THIS WAS NOT ACCEPTABLE. WE WERE UNDER THE IMPRESSION THAT OUR CTLR HAD PROPER AUTH TO ALLOW THIS DSCNT. THROUGH APPROX 4000 FT THE CTLR GAVE US A NEW FREQ FOR FLT FOLLOWING. I INFORMED HER WE NEEDED TO CONTACT DUPAGE TWR. RADAR SVC WAS TERMINATED. SHE SAID WE MADE A VERY NICE DSCNT AND WAS NEVER AWARE OF ANY PROB. WE CONTACTED DUPAGE TWR AND LANDED STRAIGHT IN RWY 28. AFTER LNDG; TWR SAID THE ZAU CTLR WISHED TO TALK TO US. CHICAGO APCH INDICATED VIOLATED CLASS B AIRSPACE. SOLUTIONS/SUGGESTIONS: 1) THE CTLR DID NOT SEEM TO UNDERSTAND OUR INTENTION OF FIRST OVERFLYING THE CLASS B BEFORE DSNDING TO DUPAGE. SHE SHOULD HAVE ASKED US TO CLARIFY. 2) THE CAPT ASKED IF WE WERE CLRED TO ENTER CLASS B. THAT SHOULD BE A YES OR NO. THE CTLR DID NOT RESPOND YES OR NO; BUT INDICATED THE ACTION WAS OK. I DO NOT UNDERSTAND HOW A CTLR CANNOT KNOW WHAT CLASS B AIRSPACE IS. 3) THE PLTS SHOULD NOT HAVE ACCEPTED THE DSCNT WITHOUT THE PROPER PHRASEOLOGY; 'CLRED TO ENTER CLASS B.' THERE ARE MANY TIMES IT IS DIFFICULT TO GET A CTLR TO SAY THE EXACT WORDS 'CLRED TO ENTER CLASS B AIRSPACE.' FREQUENTLY CTLRS JUST REPEAT THEMSELVES WITHOUT USING PROPER PHRASEOLOGY. IF CONSISTENT PHRASEOLOGY WAS REQUIRED AND ENFORCED; THIS INCIDENT COULD HAVE BEEN AVOIDED. 4) ONE OTHER FACTOR THAT I BELIEVE PLAYED A ROLE IN THIS PROB WAS THE NAME 'CHICAGO CTR' VERSUS 'CHICAGO APCH.' IT IS VERY EASY TO CONFUSE ONE CTLING AGENCY WITH ANOTHER WHEN THE FIRST NAME IS THE SAME; WHEN ACFT CHK ON TO A FREQ IT IS THE ONLY TIME THE FULL CTLING AGENCY'S NAME IS USED. EXAMPLE 'CHICAGO CTR; ACFT CALL SIGN AT 16500 FT.' IN ALL LATER XMISSIONS ONLY 'CHICAGO' WOULD BE USED TO IDENT THE ACFT'S CALL TO THE CTLR. THIS IS COMMON PRACTICE IN THE AVIATION COMMUNITY. FREQUENTLY; PLTS EVEN DROP THE NAME CTR FROM THE INITIAL CALL. I DO NOT KNOW IF THIS SHARING OF NAME CAUSED OUR PROB BECAUSE CTLRS CAN COMMUNICATE BTWN EACH OTHER TO GET AIRSPACE CLRNC; HOWEVER; 2 CTLING AGENCIES SHOULD NOT SHARE A COMMON NAME.