Narrative:

Trainee had taken handoff on air carrier X over gve VOR at FL350. Aircraft Y was northbound to gve at FL330. Trainee did not see the aircraft Y, almost head-on due to many data blocks in the area, and descended air carrier X to FL330. There was another aircraft below the air carrier X at FL310 so couldn't descend him any further. I tried to turn the aircraft but they did not answer! If the aircraft would have listened to the frequencys they would have been separated in time. Supplemental information from acn 637859: slight bumpy at FL350, asked for FL310, advised next controller would have descent clearance changed frequencys. Shortly thereafter, controller gave us a clearance to FL330. As we were descending through FL34,. The controller asked for our altitude. As I responded 'FL346 for FL330,' I observed TCASII traffic at 3 NM 10000 ft and level at FL330. I asked the controller what he wanted us to do. He responded 'turn right to 270 degrees.' I responded that we were making an immediate right turn. As we completed the turn, the controller cleared us back on course. I subsequently asked if there were any similar call signs on the frequency. The answer was no, but shortly thereafter I heard aircraft on the frequency. He was in front of us and headed for clt also. My guess is that I heard the clearance for the other aircraft to descend and thought he was calling us. I'm also speculating that my readback to the center was blocked by the other aircraft. All the speculation turned out to be incorrect, as I called ZDC after gate arrival. From the ranking supervisor I learned that we had in fact received the descent clearance but that it had been made in error. The tapes had already been reviewed and our crew was cleared of any wrong doing. While TCASII was a factor in allowing us to immediately identify the error, there were no TCASII TA's or RA's issued.

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Original NASA ASRS Text

Title: A ZDC ARTCC RADAR TRAINEE CTLR DSNDED A B737 TO AN ALT OCCUPIED BY HS25 ON A CONVERGING COURSE.

Narrative: TRAINEE HAD TAKEN HDOF ON ACR X OVER GVE VOR AT FL350. ACFT Y WAS NBOUND TO GVE AT FL330. TRAINEE DID NOT SEE THE ACFT Y, ALMOST HEAD-ON DUE TO MANY DATA BLOCKS IN THE AREA, AND DSNDED ACR X TO FL330. THERE WAS ANOTHER ACFT BELOW THE ACR X AT FL310 SO COULDN'T DSND HIM ANY FURTHER. I TRIED TO TURN THE ACFT BUT THEY DID NOT ANSWER! IF THE ACFT WOULD HAVE LISTENED TO THE FREQS THEY WOULD HAVE BEEN SEPARATED IN TIME. SUPPLEMENTAL INFO FROM ACN 637859: SLIGHT BUMPY AT FL350, ASKED FOR FL310, ADVISED NEXT CTLR WOULD HAVE DSCNT CLRNC CHANGED FREQS. SHORTLY THEREAFTER, CTLR GAVE US A CLRNC TO FL330. AS WE WERE DSNDING THROUGH FL34,. THE CTLR ASKED FOR OUR ALT. AS I RESPONDED 'FL346 FOR FL330,' I OBSERVED TCASII TFC AT 3 NM 10000 FT AND LEVEL AT FL330. I ASKED THE CTLR WHAT HE WANTED US TO DO. HE RESPONDED 'TURN R TO 270 DEGS.' I RESPONDED THAT WE WERE MAKING AN IMMEDIATE R TURN. AS WE COMPLETED THE TURN, THE CTLR CLRED US BACK ON COURSE. I SUBSEQUENTLY ASKED IF THERE WERE ANY SIMILAR CALL SIGNS ON THE FREQ. THE ANSWER WAS NO, BUT SHORTLY THEREAFTER I HEARD ACFT ON THE FREQ. HE WAS IN FRONT OF US AND HEADED FOR CLT ALSO. MY GUESS IS THAT I HEARD THE CLRNC FOR THE OTHER ACFT TO DSND AND THOUGHT HE WAS CALLING US. I'M ALSO SPECULATING THAT MY READBACK TO THE CTR WAS BLOCKED BY THE OTHER ACFT. ALL THE SPECULATION TURNED OUT TO BE INCORRECT, AS I CALLED ZDC AFTER GATE ARR. FROM THE RANKING SUPVR I LEARNED THAT WE HAD IN FACT RECEIVED THE DSCNT CLRNC BUT THAT IT HAD BEEN MADE IN ERROR. THE TAPES HAD ALREADY BEEN REVIEWED AND OUR CREW WAS CLRED OF ANY WRONG DOING. WHILE TCASII WAS A FACTOR IN ALLOWING US TO IMMEDIATELY IDENT THE ERROR, THERE WERE NO TCASII TA'S OR RA'S ISSUED.

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.