Narrative:

I cleared air carrier X for the profile descent into lax. I heard air carrier X state his call sign. Then a loud call from the speaker from lax approach control for sector 14, and finally 'runway 24/25 profile descent.' I did not hear air carrier Y call sign although it was readable on the tape. Air carrier Y read back the clearance over air carrier X transmission. Air carrier Y captain wasn't sure if the clearance was for him so he asked his copilot to verify., in reference to his question, I stated 'negative.' 15 seconds later, the conflict alert went off with traffic air carrier Z that I wasn't aware of previously. I asked air carrier Y to verify at FL200. He stated negative, he had started his descent. The 2 major causes of the incident were, air carrier Y took the clearance for air carrier X and I did not hear his call sign on the readback due to the loud speaker call in the backgnd. Air carrier Y captain was not sure if the clearance was for him. He asked to verify it and was told negative. He for some reason, then felt he had to start his descent anyway. Supplemental information from acn 149770. Air carrier Y was on descent to lax. Flight was cleared to the pmd 251/40 fix then direct fim. Flight was maintaining FL200. New center contact says 'air carrier Y verify proceeding direct fillmore.' we said were not cleared direct fillmore. He did not respond. Later he cleared us direct filmore and expect 24/25 profile descent. Next transmission we hear air carrier Y cleared profile descent. Copilot responds air carrier Y leaving FL200, center did not respond. I told the copilot I heard air carrier X and please check the clearance. We made several calls with no response from center for verification of our clearance. Finally we thought we heard a roger and since we were going direct fillmore started or descent to make our crossing restriction at fillmore (190). Center came back and said the clearance was not for us, then to maintain FL190. The center frequency was completely. Saturated the controller was not responding to radio calls at all and it seemed he was saturated and could not handle the traffic. I would like to repeat that we did call out of FL200 as 'air carrier Y leaving 200' and no response was received. Supplemental information from acn 150345. Captain started down on profile descent having misunderstood a clearance from approach. There was a similar call sign on the frequency. He asked me to confirm the descent clearance which I did and was told it was for another aircraft and for us to maintain FL200. We were out of FL190 by that time and were vectored and told to maintain FL190. No known conflict. Captain not wearing headset (and seemed hard of hearing), frequency congestion, cut first officer out of the loop.

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Original NASA ASRS Text

Title: ACR Y UNAUTH DSNT TO OCCUPIED ALT HAD LESS THAN STANDARD SEPARATION FROM ACR Z. PLTDEV.

Narrative: I CLRED ACR X FOR THE PROFILE DSNT INTO LAX. I HEARD ACR X STATE HIS CALL SIGN. THEN A LOUD CALL FROM THE SPEAKER FROM LAX APCH CTL FOR SECTOR 14, AND FINALLY 'RWY 24/25 PROFILE DSNT.' I DID NOT HEAR ACR Y CALL SIGN ALTHOUGH IT WAS READABLE ON THE TAPE. ACR Y READ BACK THE CLRNC OVER ACR X XMISSION. ACR Y CAPT WASN'T SURE IF THE CLRNC WAS FOR HIM SO HE ASKED HIS COPLT TO VERIFY., IN REFERENCE TO HIS QUESTION, I STATED 'NEGATIVE.' 15 SECS LATER, THE CONFLICT ALERT WENT OFF WITH TFC ACR Z THAT I WASN'T AWARE OF PREVIOUSLY. I ASKED ACR Y TO VERIFY AT FL200. HE STATED NEGATIVE, HE HAD STARTED HIS DSNT. THE 2 MAJOR CAUSES OF THE INCIDENT WERE, ACR Y TOOK THE CLRNC FOR ACR X AND I DID NOT HEAR HIS CALL SIGN ON THE READBACK DUE TO THE LOUD SPEAKER CALL IN THE BACKGND. ACR Y CAPT WAS NOT SURE IF THE CLRNC WAS FOR HIM. HE ASKED TO VERIFY IT AND WAS TOLD NEGATIVE. HE FOR SOME REASON, THEN FELT HE HAD TO START HIS DSNT ANYWAY. SUPPLEMENTAL INFO FROM ACN 149770. ACR Y WAS ON DSNT TO LAX. FLT WAS CLRED TO THE PMD 251/40 FIX THEN DIRECT FIM. FLT WAS MAINTAINING FL200. NEW CTR CONTACT SAYS 'ACR Y VERIFY PROCEEDING DIRECT FILLMORE.' WE SAID WERE NOT CLRED DIRECT FILLMORE. HE DID NOT RESPOND. LATER HE CLRED US DIRECT FILMORE AND EXPECT 24/25 PROFILE DSNT. NEXT XMISSION WE HEAR ACR Y CLRED PROFILE DSNT. COPLT RESPONDS ACR Y LEAVING FL200, CTR DID NOT RESPOND. I TOLD THE COPLT I HEARD ACR X AND PLEASE CHK THE CLRNC. WE MADE SEVERAL CALLS WITH NO RESPONSE FROM CTR FOR VERIFICATION OF OUR CLRNC. FINALLY WE THOUGHT WE HEARD A ROGER AND SINCE WE WERE GOING DIRECT FILLMORE STARTED OR DSNT TO MAKE OUR XING RESTRICTION AT FILLMORE (190). CTR CAME BACK AND SAID THE CLRNC WAS NOT FOR US, THEN TO MAINTAIN FL190. THE CTR FREQ WAS COMPLETELY. SATURATED THE CTLR WAS NOT RESPONDING TO RADIO CALLS AT ALL AND IT SEEMED HE WAS SATURATED AND COULD NOT HANDLE THE TFC. I WOULD LIKE TO REPEAT THAT WE DID CALL OUT OF FL200 AS 'ACR Y LEAVING 200' AND NO RESPONSE WAS RECEIVED. SUPPLEMENTAL INFO FROM ACN 150345. CAPT STARTED DOWN ON PROFILE DSNT HAVING MISUNDERSTOOD A CLRNC FROM APCH. THERE WAS A SIMILAR CALL SIGN ON THE FREQ. HE ASKED ME TO CONFIRM THE DSNT CLRNC WHICH I DID AND WAS TOLD IT WAS FOR ANOTHER ACFT AND FOR US TO MAINTAIN FL200. WE WERE OUT OF FL190 BY THAT TIME AND WERE VECTORED AND TOLD TO MAINTAIN FL190. NO KNOWN CONFLICT. CAPT NOT WEARING HEADSET (AND SEEMED HARD OF HEARING), FREQ CONGESTION, CUT F/O OUT OF THE LOOP.

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.