Narrative:

Air carrier X off denver, requesting FL370, was cleared to FL330 for traffic. Air carrier X acknowledged the clearance with the original controller and the next controller. The conflict alert flashed and the data block of air carrier X was observed past the traffic and climbing through FL340. No evasive clearance was issued since the traffic had passed. I don't know what caused it. Speculation is air carrier X took a clearance for another aircraft and his readback was completely covered by the aircraft the clearance was intended for. Supplemental information from acn 118961: received clearance to FL370 from ZDV. Acknowledged clearance and began climb to 370. No response from the center. Leaving FL340, denver controller asked our altitude. Responded 'leaving FL340 for 370'. No center response. Conflicting traffic passed on our left, well clear, at FL350 going wbound (1000' above and approximately 4 mi horizontal from our position). Leaving FL350, controller cleared us to climb to FL370. We acknowledged 'climb to FL370'. Controller's calls were 'scratchy-but readable.' he was working other aircraft on different frequencys. We read his xmissions to other aircraft but not their acknowledgements, only those on our frequency. Another aircraft had a similar call sign. After landing at destination, I learned from the violations coordinator at ZDV that: 1) tape had been pulled and read. 2) controller was working at least 3 different frequencys. 3) controller did not receive our acknowledgement of the clearance to FL370 nor of any other aircraft, more than one aircraft, on different frequencys, had responded and the tape was garbled. 4) there was conflicting wbound traffic at 350. Supplemental information from acn 119179: I was flying the aircraft, autoplt engaged, the captain was working the radios. ZDV issued a clearance '(flight #) climb maintain 370'. I heard '(garble) eight' as the flight identification, the captain later said he thought he heard the whole flight number. The F/east said he heard only the 'eight'. The air carrier was not heard by anyone. Eight was the last digit of our 3 digit flight number.

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Original NASA ASRS Text

Title: FLT CREW OF ACR A CLIMBED FROM ASSIGNED ALT THROUGH ACR B'S ALT WITHOUT CLRNC. PLT DEVIATION. LESS THAN STANDARD SEPARATION.

Narrative: ACR X OFF DENVER, REQUESTING FL370, WAS CLRED TO FL330 FOR TFC. ACR X ACKNOWLEDGED THE CLRNC WITH THE ORIGINAL CTLR AND THE NEXT CTLR. THE CONFLICT ALERT FLASHED AND THE DATA BLOCK OF ACR X WAS OBSERVED PAST THE TFC AND CLIMBING THROUGH FL340. NO EVASIVE CLRNC WAS ISSUED SINCE THE TFC HAD PASSED. I DON'T KNOW WHAT CAUSED IT. SPECULATION IS ACR X TOOK A CLRNC FOR ANOTHER ACFT AND HIS READBACK WAS COMPLETELY COVERED BY THE ACFT THE CLRNC WAS INTENDED FOR. SUPPLEMENTAL INFORMATION FROM ACN 118961: RECEIVED CLRNC TO FL370 FROM ZDV. ACKNOWLEDGED CLRNC AND BEGAN CLIMB TO 370. NO RESPONSE FROM THE CENTER. LEAVING FL340, DENVER CTLR ASKED OUR ALT. RESPONDED 'LEAVING FL340 FOR 370'. NO CENTER RESPONSE. CONFLICTING TFC PASSED ON OUR LEFT, WELL CLEAR, AT FL350 GOING WBOUND (1000' ABOVE AND APPROX 4 MI HORIZ FROM OUR POSITION). LEAVING FL350, CTLR CLRED US TO CLIMB TO FL370. WE ACKNOWLEDGED 'CLIMB TO FL370'. CTLR'S CALLS WERE 'SCRATCHY-BUT READABLE.' HE WAS WORKING OTHER ACFT ON DIFFERENT FREQS. WE READ HIS XMISSIONS TO OTHER ACFT BUT NOT THEIR ACKNOWLEDGEMENTS, ONLY THOSE ON OUR FREQ. ANOTHER ACFT HAD A SIMILAR CALL SIGN. AFTER LNDG AT DEST, I LEARNED FROM THE VIOLATIONS COORDINATOR AT ZDV THAT: 1) TAPE HAD BEEN PULLED AND READ. 2) CTLR WAS WORKING AT LEAST 3 DIFFERENT FREQS. 3) CTLR DID NOT RECEIVE OUR ACKNOWLEDGEMENT OF THE CLRNC TO FL370 NOR OF ANY OTHER ACFT, MORE THAN ONE ACFT, ON DIFFERENT FREQS, HAD RESPONDED AND THE TAPE WAS GARBLED. 4) THERE WAS CONFLICTING WBOUND TFC AT 350. SUPPLEMENTAL INFORMATION FROM ACN 119179: I WAS FLYING THE ACFT, AUTOPLT ENGAGED, THE CAPT WAS WORKING THE RADIOS. ZDV ISSUED A CLRNC '(FLT #) CLIMB MAINTAIN 370'. I HEARD '(GARBLE) EIGHT' AS THE FLT IDENTIFICATION, THE CAPT LATER SAID HE THOUGHT HE HEARD THE WHOLE FLT NUMBER. THE F/E SAID HE HEARD ONLY THE 'EIGHT'. THE AIR CARRIER WAS NOT HEARD BY ANYONE. EIGHT WAS THE LAST DIGIT OF OUR 3 DIGIT FLT NUMBER.

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.