Narrative:

Air carrier X from iah to tul. Large transport leveled at FL330. We were told our descent would be in a few after passing traffic. A few mins later, center gave us clearance to FL210. I read back the clearance to descend to FL210 and the captain (PF) started his descent. Out of 29700' the controller asked our altitude and I responded FL297. He asked our clearance altitude and I said FL210. He replied clearance was FL310 and we returned to FL310. I responded that we read back the clearance to FL210 and all 3 crew members plus a jump seat rider overhead his clearance and my readback. There was no reply from the controller. Supplemental information from acn 174174: air carrier X cleared from 33000 to 21000'. At 29700' center said we had traffic 1 mi at 28000'. I immediately stopped descent and started a climb. Center said our altitude was supposed to be 31000'. We continued climb to 31000'. We never saw the traffic. On the initial descent clearance we read back 21000' the center controller mentioned an air carrier aircraft below us that was also headed for tul. We were faster and would descend through his altitude.

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Original NASA ASRS Text

Title: ACR X HAD LESS THAN STANDARD SEPARATION FROM ACFT Y. SYSTEM ERROR. ACR X DESCENT TO WRONG ALT, NON ADHERENCE TO ATC INSTRUCTIONS.

Narrative: ACR X FROM IAH TO TUL. LGT LEVELED AT FL330. WE WERE TOLD OUR DSNT WOULD BE IN A FEW AFTER PASSING TFC. A FEW MINS LATER, CENTER GAVE US CLRNC TO FL210. I READ BACK THE CLRNC TO DSND TO FL210 AND THE CAPT (PF) STARTED HIS DSNT. OUT OF 29700' THE CTLR ASKED OUR ALT AND I RESPONDED FL297. HE ASKED OUR CLRNC ALT AND I SAID FL210. HE REPLIED CLRNC WAS FL310 AND WE RETURNED TO FL310. I RESPONDED THAT WE READ BACK THE CLRNC TO FL210 AND ALL 3 CREW MEMBERS PLUS A JUMP SEAT RIDER OVERHEAD HIS CLRNC AND MY READBACK. THERE WAS NO REPLY FROM THE CTLR. SUPPLEMENTAL INFO FROM ACN 174174: ACR X CLRED FROM 33000 TO 21000'. AT 29700' CENTER SAID WE HAD TFC 1 MI AT 28000'. I IMMEDIATELY STOPPED DSNT AND STARTED A CLB. CENTER SAID OUR ALT WAS SUPPOSED TO BE 31000'. WE CONTINUED CLB TO 31000'. WE NEVER SAW THE TFC. ON THE INITIAL DSNT CLRNC WE READ BACK 21000' THE CENTER CTLR MENTIONED AN ACR ACFT BELOW US THAT WAS ALSO HEADED FOR TUL. WE WERE FASTER AND WOULD DSND THROUGH HIS ALT.

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.