Narrative:

While operating a scheduled flight as first officer and PF; the captain acknowledged and read back a clearance to FL240. We were at FL280. We started our descent promptly and were approximately FL275 when ATC inquired why we were descending. After verifying 'yes' he gave us an immediate left turn 30 degrees. We made the turn at the same time we got a TCAS advisory. We spotted the traffic visually as well as on the TCAS. At this time he cleared us to FL280 again. He asked us if we received descent clearance from a previous controller. We responded that it was him that cleared us lower. Soon after this incident we were told to switch frequency.

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Original NASA ASRS Text

Title: CL600 FLT CREW IS ISSUED A DSCNT CLRNC AND RECEIVES TCAS ALERT DURING DSCNT.

Narrative: WHILE OPERATING A SCHEDULED FLT AS FO AND PF; THE CAPT ACKNOWLEDGED AND READ BACK A CLRNC TO FL240. WE WERE AT FL280. WE STARTED OUR DSCNT PROMPTLY AND WERE APPROX FL275 WHEN ATC INQUIRED WHY WE WERE DSNDING. AFTER VERIFYING 'YES' HE GAVE US AN IMMEDIATE L TURN 30 DEGS. WE MADE THE TURN AT THE SAME TIME WE GOT A TCAS ADVISORY. WE SPOTTED THE TFC VISUALLY AS WELL AS ON THE TCAS. AT THIS TIME HE CLRED US TO FL280 AGAIN. HE ASKED US IF WE RECEIVED DSCNT CLRNC FROM A PREVIOUS CTLR. WE RESPONDED THAT IT WAS HIM THAT CLRED US LOWER. SOON AFTER THIS INCIDENT WE WERE TOLD TO SWITCH FREQ.

Data retrieved from NASA's ASRS site as of January 2009 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.