AN ERJ-145 FLT CREW EXCEEDED THEIR ASSIGNED ALT BY 200 FT WHEN THEY THOUGHT THEY WERE CLRED TO FL230 BUT ATC ASSIGNED 13000 FT.

Narrative

MY FO AND I WERE CLBING OUT OF DETROIT ON A CLR CALM NIGHT. DEP CTL ISSUED US A CLRNC OF DIRECT TO CAVVS INTXN; ON A 230 DEG HDG; AND CLB TO FL230. AFTER READING BACK THE CLRNC; I LEFT RADIO #1 TO RPT OUR OUT AND OFF TIMES. I RETURNED TO RADIO #1 APPROX 1 MIN LATER. MY FO TOLD ME TO CONTACT THE NEXT CTR FREQ. HE HAD NOT CHKED ON WITH THEM. I TOLD CTR THAT WE WERE CLBING OUT OF 13000 FT FOR FL230. AT THAT POINT HE ASKED WHO HAD GIVEN US FL230. I TOLD HIM THE PREVIOUS CTLR. HE THEN STATED WE WERE ONLY CLRED TO 13000 FT. MY FO LEVELED THE ACFT AT 13200 FT AND IMMEDIATELY STARTED A DSCNT BACK TO 13000 FT. AT NO POINT DID OUR TCASII SHOW ANY KIND OF TFC ALERT. WE CONTINUED ON TO DEST WITHOUT INCIDENT. AFTER CHKING ON WITH ZTL; WE WERE NOTIFIED OF A POSSIBLE ALTDEV IN DETROIT. WE WERE GIVEN A PHONE NUMBER WITH OUR CLRNC. WE LANDED WITHOUT INCIDENT. SUPPLEMENTAL INFO FROM ACN 587660: ZTL TOLD US THAT THERE HAD BEEN LOSS OF ACFT SEPARATION DUE TO THE INCIDENT AND WE HAD BEEN RPTED. READBACK SHOULD HAVE BEEN CHALLENGED AND CORRECTED. IT TURNS OUT THAT HE WANTED US TO STAY AT 13000 FT AND FLY A 230 DEG HDG AND PROCEED DIRECT CAVVS WHEN ABLE. ATC CLAIMS THERE WAS A 400 FT DEV; BUT WE SHOWED 200 FT ON OUR ALTIMETER. WE NEVER GOT A TCASII TA OR RA. CONCLUSION: FAILURE BY ATC TO CORRECT AN INCORRECT READBACK OF A CLRNC RESULTED IN OUR ALTDEV AND THUS; LOSS OF ACFT SEPARATION.