Narrative:

I was working air carrier X outbound from atlanta, GA en route to columbia, sc, when air carrier X checked on frequency I cleared him to FL230, paused with microphone still keyed, and then corrected to 17000 ft restated the call sign and issued a heading. The pilot acknowledged with a roger and restated the heading. I issued merging target procedures to air carrier X at 15 NM and 8 NM from the traffic at FL180. When the 2 aircraft were 5 NM apart I observed air carrier X above assigned altitude, and asked him to verify leveling 17000 ft. He responded in the negative 'climbing to FL230'. I then issued an immediate descent clearance to 17000 ft and issued the traffic. I believe the pilot keyed his microphone and acknowledged clearance to FL230 while I was correcting his assigned altitude therefore never hearing the correction, and unkeyed in time to hear his call sign and assigned heading. I do not believe there is any way to prevent the frequency, simultaneously transmitting, however I find it difficult to understand why air carrier X crew did not question their assigned altitude with the issuance of traffic at FL180. Pilots (crew) need to take a more active role in the 'checks and balances' for safety sake. Supplemental information from acn 180403: air carrier X after takeoff, while climbing to flight planned altitude and flying direct to the cae VOR, we were handed off to atlanta center frequency 124.45. After checking in on the frequency we were cleared to climb to FL230. Center then called out traffic, small transport Y at FL180, 2 O'clock, 12 mi. Subsequently we were given a heading of 070 degree. I acknowledged heading 070 degree for higher. I thought it was a vector for our climb. Traffic was again called out at 1 O'clock 8-10 mi FL180. I asked the captain, 'why he keeps calling traffic - we'll be at FL230 by the time small transport Y gets near us'. As we passed 17600 ft center called and asked us to confirm our assigned altitude was 17000 ft. I responded negative we were cleared to FL230. Center then gave us an immediate descent to 17000 ft and said we had traffic at 12 O'clock, FL180, 5 mi. I said we were descending to 17000 and we had the traffic in sight. In my opinion the heading assignment caused a lot of confusion in this situation and a simple altitude assignment would have been the better course of action. The 070 degree heading led me to believe that we would remain clear of the traffic while climbed to FL230. Neither the captain nor I remember hearing 17000 ft as our assigned altitude, nor did we acknowledge 17000 ft to the center, nor did we enter 17000 ft in the altitude reminder (23000 ft was set in the altitude reminder at the time of the conflict).

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Original NASA ASRS Text

Title: ACR X HAD LTSS FROM SMT Y. SYS ERROR.

Narrative: I WAS WORKING ACR X OUTBOUND FROM ATLANTA, GA ENRTE TO COLUMBIA, SC, WHEN ACR X CHKED ON FREQ I CLRED HIM TO FL230, PAUSED WITH MICROPHONE STILL KEYED, AND THEN CORRECTED TO 17000 FT RESTATED THE CALL SIGN AND ISSUED A HDG. THE PLT ACKNOWLEDGED WITH A ROGER AND RESTATED THE HDG. I ISSUED MERGING TARGET PROCS TO ACR X AT 15 NM AND 8 NM FROM THE TFC AT FL180. WHEN THE 2 ACFT WERE 5 NM APART I OBSERVED ACR X ABOVE ASSIGNED ALT, AND ASKED HIM TO VERIFY LEVELING 17000 FT. HE RESPONDED IN THE NEGATIVE 'CLBING TO FL230'. I THEN ISSUED AN IMMEDIATE DSCNT CLRNC TO 17000 FT AND ISSUED THE TFC. I BELIEVE THE PLT KEYED HIS MICROPHONE AND ACKNOWLEDGED CLRNC TO FL230 WHILE I WAS CORRECTING HIS ASSIGNED ALT THEREFORE NEVER HEARING THE CORRECTION, AND UNKEYED IN TIME TO HEAR HIS CALL SIGN AND ASSIGNED HDG. I DO NOT BELIEVE THERE IS ANY WAY TO PREVENT THE FREQ, SIMULTANEOUSLY XMITTING, HOWEVER I FIND IT DIFFICULT TO UNDERSTAND WHY ACR X CREW DID NOT QUESTION THEIR ASSIGNED ALT WITH THE ISSUANCE OF TFC AT FL180. PLTS (CREW) NEED TO TAKE A MORE ACTIVE ROLE IN THE 'CHKS AND BALANCES' FOR SAFETY SAKE. SUPPLEMENTAL INFO FROM ACN 180403: ACR X AFTER TKOF, WHILE CLBING TO FLT PLANNED ALT AND FLYING DIRECT TO THE CAE VOR, WE WERE HANDED OFF TO ATLANTA CENTER FREQ 124.45. AFTER CHKING IN ON THE FREQ WE WERE CLRED TO CLB TO FL230. CENTER THEN CALLED OUT TFC, SMT Y AT FL180, 2 O'CLOCK, 12 MI. SUBSEQUENTLY WE WERE GIVEN A HDG OF 070 DEG. I ACKNOWLEDGED HDG 070 DEG FOR HIGHER. I THOUGHT IT WAS A VECTOR FOR OUR CLB. TFC WAS AGAIN CALLED OUT AT 1 O'CLOCK 8-10 MI FL180. I ASKED THE CAPT, 'WHY HE KEEPS CALLING TFC - WE'LL BE AT FL230 BY THE TIME SMT Y GETS NEAR US'. AS WE PASSED 17600 FT CENTER CALLED AND ASKED US TO CONFIRM OUR ASSIGNED ALT WAS 17000 FT. I RESPONDED NEGATIVE WE WERE CLRED TO FL230. CENTER THEN GAVE US AN IMMEDIATE DSCNT TO 17000 FT AND SAID WE HAD TFC AT 12 O'CLOCK, FL180, 5 MI. I SAID WE WERE DSNDING TO 17000 AND WE HAD THE TFC IN SIGHT. IN MY OPINION THE HDG ASSIGNMENT CAUSED A LOT OF CONFUSION IN THIS SITUATION AND A SIMPLE ALT ASSIGNMENT WOULD HAVE BEEN THE BETTER COURSE OF ACTION. THE 070 DEG HDG LED ME TO BELIEVE THAT WE WOULD REMAIN CLR OF THE TFC WHILE CLIMBED TO FL230. NEITHER THE CAPT NOR I REMEMBER HEARING 17000 FT AS OUR ASSIGNED ALT, NOR DID WE ACKNOWLEDGE 17000 FT TO THE CENTER, NOR DID WE ENTER 17000 FT IN THE ALT REMINDER (23000 FT WAS SET IN THE ALT REMINDER AT THE TIME OF THE CONFLICT).

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.