MD80 FLT CREW SET INCORRECT ALT IN ALT ALERT WHILE CONDUCTING RNAV ARRIVAL AND DESCENDED THROUGH THE ASSIGNED ALT.

Narrative

WE WERE APCHING ATL FROM THE SW; ON THE HONIE 5 ARR; AT 14000 FT MSL AND LESS THAN 50 MI FROM THE ARPT. THE COPLT WAS THE PLT AT THE CTLS; BRIEFING AN EXPECTED APCH TO RWY 27L. ATL APCH CTL ADVISED US TO EXPECT RWY 26R AND ISSUED A CLRNC TO SET UP FOR THE WAYPOINTS ASSOCIATED WITH A N RWY COMPLEX ARR. AS WE PASSED HONIE INTXN AT AN ASSIGNED AIRSPD OF 250 KTS; WE WERE INSTRUCTED TO DELETE WOLMN INTXN AND PROCEED FROM TIROE INTXN TO NOFIV INTXN. RELIEF FROM SPD RESTRS ASSOCIATED WITH THE ARR WAS ALSO GIVEN BY ATC AND WE COMPLIED WITH INSTRUCTIONS TO ACCELERATE AND MAINTAIN BEST FORWARD AIRSPD. THE COPLT REVIEWED THE POINTS ON THE ARR PLATE FOR THE N ARR AND BEGAN BRIEFING THE APCH TO RWY 26R. ATL APCH CTL DIRECTED A DSCNT TO 12000 FT; ASSIGNED A HDG OF 030 DEGS; AND INSTRUCTED US TO REJOIN THE ARR PRIOR TO FANEW INTXN. I READ BACK THE CLRNC TO 12000 FT. THE COPLT THOUGHT THE CLRNC WAS TO 10000 FT; POSSIBLY MISTAKING A CLRNC FOR ANOTHER ACFT; AND SET 10000 FT IN THE ALT ALERTER. WE RETURNED TO COMPLETING THE APCH BRIEF; VERIFYING CHANGES IN THE FMS AND OTHER SETTINGS; AND REVIEWING THE DSCNT CHKLIST WITHOUT COMPLETING THE DOUBLE-POINT PROC TO VERIFY THE CLRNC ALT. ATL APCH CTL ALERTED US AS WE DSNDED THROUGH 11000 FT MSL; AND DIRECTED A CLB BACK TO 11000 FT. WHEN QUERIED; I ERRONEOUSLY RPTED THAT WE HAD BEEN CLRED TO 10000 FT. A FOLLOW-UP TELEPHONE CONVERSATION WITH ATL TRACON VERIFIED THAT WE HAD RECEIVED CLRNC TO 12000 FT; AND I HAD READ BACK 12000 FT. TRACON ALSO ADVISED ME THAT THERE HAD BEEN NO TFC CONFLICT.