Narrative:

We were tracking inbound on the 086 degree right with clearance to turn right to 290 degrees at the 12 DME fix. We were beyond 12 mi at 7000' MSL at which time a clearance was issued to descend to 4000' and slow to 170 KTS. I didn't specifically hear our call sign, but thought I may have missed it while the captain heard it. The captain acknowledged the clearance with our call sign and no response was received from approach. The 2 mistakes here were the failure of the controller to listen to the readback and me missing the call sign and failing to ask the captain to verify that the call was for us. The clearance was, in fact, for another aircraft. At about 5 mi from the airport on a left downwind for 11L while descending through 4500 for 4000', the controller asked our altitude and we responded. He told us our assigned altitude was 7000' and we had traffic at 11-12 O'clock climbing out of 5500'. I don't specifically remember what range the controller gave, but I estimate 3-4 mi. We saw the small aircraft and there was no imminent danger of collision. End of incident. I feel the greatest contributing factor was the failure of the controller to listen to the readback. Controllers are often on land lines or talking with aircraft on other frequencys due to the higher workload due to the relative shortage of controllers. This definitely compromises safety for the very reason of this incident. I did not question the captain as to the proper call sign because I was not sure if it was incorrect. I wrongly assumed it was for us because the controller did not challenge our readback. The problem is in the fact that very often one of the pilots does not hear the call sign while the other does, so there is no chance of positively confirming the transaction unless the controller acknowledges the readback. We probably rely too much on the controller properly listening to the readback which fails to happen all too often. Call signs are missed by one or both pilots often due to several reasons including controller use of clipped call signs, second officer talking during the initial transmission, other distrs in the cockpit, or something as simple as clearing your throat. Corrective actions I might suggest are adding more controllers and reducing their off frequency workload, increased radio vigilance on the part of both pilots and controllers, using clear and distinct call signs even when very heavy radio traffic occurs, and questioning if there is any doubt whatsoever.

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Original NASA ASRS Text

Title: LGT LEFT ASSIGNED ALT.

Narrative: WE WERE TRACKING INBND ON THE 086 DEG R WITH CLRNC TO TURN RIGHT TO 290 DEGS AT THE 12 DME FIX. WE WERE BEYOND 12 MI AT 7000' MSL AT WHICH TIME A CLRNC WAS ISSUED TO DSND TO 4000' AND SLOW TO 170 KTS. I DIDN'T SPECIFICALLY HEAR OUR CALL SIGN, BUT THOUGHT I MAY HAVE MISSED IT WHILE THE CAPT HEARD IT. THE CAPT ACKNOWLEDGED THE CLRNC WITH OUR CALL SIGN AND NO RESPONSE WAS RECEIVED FROM APCH. THE 2 MISTAKES HERE WERE THE FAILURE OF THE CTLR TO LISTEN TO THE READBACK AND ME MISSING THE CALL SIGN AND FAILING TO ASK THE CAPT TO VERIFY THAT THE CALL WAS FOR US. THE CLRNC WAS, IN FACT, FOR ANOTHER ACFT. AT ABOUT 5 MI FROM THE ARPT ON A LEFT DOWNWIND FOR 11L WHILE DSNDING THROUGH 4500 FOR 4000', THE CTLR ASKED OUR ALT AND WE RESPONDED. HE TOLD US OUR ASSIGNED ALT WAS 7000' AND WE HAD TFC AT 11-12 O'CLOCK CLBING OUT OF 5500'. I DON'T SPECIFICALLY REMEMBER WHAT RANGE THE CTLR GAVE, BUT I ESTIMATE 3-4 MI. WE SAW THE SMA AND THERE WAS NO IMMINENT DANGER OF COLLISION. END OF INCIDENT. I FEEL THE GREATEST CONTRIBUTING FACTOR WAS THE FAILURE OF THE CTLR TO LISTEN TO THE READBACK. CTLRS ARE OFTEN ON LAND LINES OR TALKING WITH ACFT ON OTHER FREQS DUE TO THE HIGHER WORKLOAD DUE TO THE RELATIVE SHORTAGE OF CTLRS. THIS DEFINITELY COMPROMISES SAFETY FOR THE VERY REASON OF THIS INCIDENT. I DID NOT QUESTION THE CAPT AS TO THE PROPER CALL SIGN BECAUSE I WAS NOT SURE IF IT WAS INCORRECT. I WRONGLY ASSUMED IT WAS FOR US BECAUSE THE CTLR DID NOT CHALLENGE OUR READBACK. THE PROB IS IN THE FACT THAT VERY OFTEN ONE OF THE PLTS DOES NOT HEAR THE CALL SIGN WHILE THE OTHER DOES, SO THERE IS NO CHANCE OF POSITIVELY CONFIRMING THE TRANSACTION UNLESS THE CTLR ACKNOWLEDGES THE READBACK. WE PROBABLY RELY TOO MUCH ON THE CTLR PROPERLY LISTENING TO THE READBACK WHICH FAILS TO HAPPEN ALL TOO OFTEN. CALL SIGNS ARE MISSED BY ONE OR BOTH PLTS OFTEN DUE TO SEVERAL REASONS INCLUDING CTLR USE OF CLIPPED CALL SIGNS, S/O TALKING DURING THE INITIAL XMISSION, OTHER DISTRS IN THE COCKPIT, OR SOMETHING AS SIMPLE AS CLEARING YOUR THROAT. CORRECTIVE ACTIONS I MIGHT SUGGEST ARE ADDING MORE CTLRS AND REDUCING THEIR OFF FREQ WORKLOAD, INCREASED RADIO VIGILANCE ON THE PART OF BOTH PLTS AND CTLRS, USING CLEAR AND DISTINCT CALL SIGNS EVEN WHEN VERY HEAVY RADIO TFC OCCURS, AND QUESTIONING IF THERE IS ANY DOUBT WHATSOEVER.

Data retrieved from NASA's ASRS site as of August 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.