Narrative:

Flight from las to phx cruising at FL290 on STAR karlo 6 bld transition. ZAB vectored us off the arrival. PNF (captain) went momentarily off frequency and returned to hear PF (first officer) acknowledge descent clearance to FL240. PF then repeated the clearance to PNF as direct karlo and down to FL240. During the descending turn, TCASII TA indicated traffic at 4 O'clock position moving away 600 ft below. Center asked if we were still at FL290, PNF responded negative, descending through FL276. ATC stated that we should be at FL290 until clear of traffic, then cleared us to FL240. The PF reported afterwards that ATC issued clearance of direct karlo, descend to FL240, and traffic at 12 O'clock position. PF read back direct karlo, descend to FL240, then began the right descending turn. Center indicated a possible conflict and gave us a phone number to call. The watch supervisor in the subsequent conversation with ARTCC said the controller cleared us direct karlo and to maintain FL290. If this is true, then my suggestion would be that controllers not include a statement in a clearance to maintain the altitude a pilot is maintaining anyway. In this case, we were held high and the PF was expecting to be cleared for a descent. When the controller mentioned the traffic, the PF reasoned that was why this controller held us up, but given the turn, there would be no conflict now for a descent. The controller on the other hand would be less apt to listen for a descent clearance readback when he had just presumably said to maintain FL290. I suggest that at no time should a controller reiterate a clearance that the pilot has already complied with. This can only open opportunity for error.

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Original NASA ASRS Text

Title: AN A320 ACR AT FL290 WAS VECTORED OFF THE KARLO SIX STAR FOR TFC. WHEN ARTCC RECLRED ACR BACK TO STAR, THE PF ASSUMED THEY HAD DSCNT CLRNC TO FL240 AND STARTED DSCNT. THE ACR RECEIVED A TCASII TA, OBSERVING TFC PASSING 600 FT BELOW THEM. ATC ASKED ACR TO VERIFY AT FL290 AND ACR ADVISED THEY WERE DSNDING THROUGH FL267. ATC ADVISED THEY HAD COME IN CONFLICT WITH ANOTHER ACFT AND WAS ASKED TO CALL ARTCC UPON LNDG.

Narrative: FLT FROM LAS TO PHX CRUISING AT FL290 ON STAR KARLO 6 BLD TRANSITION. ZAB VECTORED US OFF THE ARR. PNF (CAPT) WENT MOMENTARILY OFF FREQ AND RETURNED TO HEAR PF (FO) ACKNOWLEDGE DSCNT CLRNC TO FL240. PF THEN REPEATED THE CLRNC TO PNF AS DIRECT KARLO AND DOWN TO FL240. DURING THE DSNDING TURN, TCASII TA INDICATED TFC AT 4 O'CLOCK POS MOVING AWAY 600 FT BELOW. CTR ASKED IF WE WERE STILL AT FL290, PNF RESPONDED NEGATIVE, DSNDING THROUGH FL276. ATC STATED THAT WE SHOULD BE AT FL290 UNTIL CLR OF TFC, THEN CLRED US TO FL240. THE PF RPTED AFTERWARDS THAT ATC ISSUED CLRNC OF DIRECT KARLO, DSND TO FL240, AND TFC AT 12 O'CLOCK POS. PF READ BACK DIRECT KARLO, DSND TO FL240, THEN BEGAN THE R DSNDING TURN. CTR INDICATED A POSSIBLE CONFLICT AND GAVE US A PHONE NUMBER TO CALL. THE WATCH SUPVR IN THE SUBSEQUENT CONVERSATION WITH ARTCC SAID THE CTLR CLRED US DIRECT KARLO AND TO MAINTAIN FL290. IF THIS IS TRUE, THEN MY SUGGESTION WOULD BE THAT CTLRS NOT INCLUDE A STATEMENT IN A CLRNC TO MAINTAIN THE ALT A PLT IS MAINTAINING ANYWAY. IN THIS CASE, WE WERE HELD HIGH AND THE PF WAS EXPECTING TO BE CLRED FOR A DSCNT. WHEN THE CTLR MENTIONED THE TFC, THE PF REASONED THAT WAS WHY THIS CTLR HELD US UP, BUT GIVEN THE TURN, THERE WOULD BE NO CONFLICT NOW FOR A DSCNT. THE CTLR ON THE OTHER HAND WOULD BE LESS APT TO LISTEN FOR A DSCNT CLRNC READBACK WHEN HE HAD JUST PRESUMABLY SAID TO MAINTAIN FL290. I SUGGEST THAT AT NO TIME SHOULD A CTLR REITERATE A CLRNC THAT THE PLT HAS ALREADY COMPLIED WITH. THIS CAN ONLY OPEN OPPORTUNITY FOR ERROR.

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.