Narrative:

We were beginning our descent into the chicago area. We were given pilot's discretion to 17000 ft and told to expect jolet VOR at 6000 ft. We were currently at FL240. We switched to a different controller and I checked in with 'FL240 discretion to 17000 ft' which the controller acknowledged. Shortly after that the controller said 'descend now to FL210.' we started our descent and began to experience continuous chop. Also we were approaching our descent point on the moving map, so the captain continued with the descent to 17000 ft, which we thought we still had clearance to. The controller immediately began to question our descent because of traffic at FL200. We also received an RA from TCASII which we complied with and were back at FL210 prior to visually acquiring the other aircraft. The controller either did not realize we had discretion to 17000 ft or forgot, but he never canceled that clearance. 'Descend now to FL210' does not cancel the clearance to 17000 ft. Better communication between sector controllers (ie, handoff clrncs) and better communication between pilot and controller would have prevented this occurrence. Controllers need to use the proper verbiage if they want to cancel a clearance. Supplemental information from acn 427152: we were in level cruise flight at FL200 cleared direct our destination of cedar rapids, ia, when we received a TCASII TA. About the same time ZAU began to inquire about an air carrier airliner's altitude assignment. Shortly after the TA we received an RA to climb rapidly. We got visual contact and heard the air carrier say they were going to climb. So we said we were descending. We descended about 200 ft when the TCASII alert stopped. At this point our TCASII indicated conflicting traffic was more than 1000 ft above us and level. We then returned to our altitude as the B737 passed directly above us.

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Original NASA ASRS Text

Title: B737 AND CL65 HAD LESS THAN LEGAL SEPARATION.

Narrative: WE WERE BEGINNING OUR DSCNT INTO THE CHICAGO AREA. WE WERE GIVEN PLT'S DISCRETION TO 17000 FT AND TOLD TO EXPECT JOLET VOR AT 6000 FT. WE WERE CURRENTLY AT FL240. WE SWITCHED TO A DIFFERENT CTLR AND I CHKED IN WITH 'FL240 DISCRETION TO 17000 FT' WHICH THE CTLR ACKNOWLEDGED. SHORTLY AFTER THAT THE CTLR SAID 'DSND NOW TO FL210.' WE STARTED OUR DSCNT AND BEGAN TO EXPERIENCE CONTINUOUS CHOP. ALSO WE WERE APCHING OUR DSCNT POINT ON THE MOVING MAP, SO THE CAPT CONTINUED WITH THE DSCNT TO 17000 FT, WHICH WE THOUGHT WE STILL HAD CLRNC TO. THE CTLR IMMEDIATELY BEGAN TO QUESTION OUR DSCNT BECAUSE OF TFC AT FL200. WE ALSO RECEIVED AN RA FROM TCASII WHICH WE COMPLIED WITH AND WERE BACK AT FL210 PRIOR TO VISUALLY ACQUIRING THE OTHER ACFT. THE CTLR EITHER DID NOT REALIZE WE HAD DISCRETION TO 17000 FT OR FORGOT, BUT HE NEVER CANCELED THAT CLRNC. 'DSND NOW TO FL210' DOES NOT CANCEL THE CLRNC TO 17000 FT. BETTER COM BTWN SECTOR CTLRS (IE, HDOF CLRNCS) AND BETTER COM BTWN PLT AND CTLR WOULD HAVE PREVENTED THIS OCCURRENCE. CTLRS NEED TO USE THE PROPER VERBIAGE IF THEY WANT TO CANCEL A CLRNC. SUPPLEMENTAL INFO FROM ACN 427152: WE WERE IN LEVEL CRUISE FLT AT FL200 CLRED DIRECT OUR DEST OF CEDAR RAPIDS, IA, WHEN WE RECEIVED A TCASII TA. ABOUT THE SAME TIME ZAU BEGAN TO INQUIRE ABOUT AN ACR AIRLINER'S ALT ASSIGNMENT. SHORTLY AFTER THE TA WE RECEIVED AN RA TO CLB RAPIDLY. WE GOT VISUAL CONTACT AND HEARD THE ACR SAY THEY WERE GOING TO CLB. SO WE SAID WE WERE DSNDING. WE DSNDED ABOUT 200 FT WHEN THE TCASII ALERT STOPPED. AT THIS POINT OUR TCASII INDICATED CONFLICTING TFC WAS MORE THAN 1000 FT ABOVE US AND LEVEL. WE THEN RETURNED TO OUR ALT AS THE B737 PASSED DIRECTLY ABOVE US.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.