ACR CLIMBED ABOVE ALT INTENDED BY ATC. OPERATIONAL DEVIATION.

Narrative

I WAS MONITORING MY TRNEE DURING A MODERATE TFC PERIOD. AN AIR CARRIER DEPARTED RWY 23 AT MC GHEE TYSON ARPT. THE ACFT WAS RWY HDG CLBING TO 6000'. MY TRNEE INSTRUCTED THE ACFT TO TURN LEFT HDG 1-1-0 AND TO CLB AND MAINTAIN 1-0-THOUSAND. LATER; AS MY TRNEE WAS CHANGING THE ACFT TO ATL CENTER FREQ; WE NOTICED THE ACFT STARTING TO CLB OUT OF 10000'. WE INSTRUCTED THE ACFT TO MAINTAIN 1-0-THOUSAND. THE ACFT ENDED UP AT 1-1-THOUSAND. HIGHER ALT WAS OBTAINED FROM ATL CENTER AND THE ACFT WAS CHANGED (FREQ) TO THEM. THE FAC MGR WAS NEXT TO US IN THE TRACON AT THE TIME. HE AND I REVIEWED THE TAPE. WE (MY TRNEE) HAD ISSUED THE CORRECT ALT; BUT THE PLT HAD READ BACK HDG 1-1-0 AND MAINTAIN 1-1-THOUSAND. NEITHER THE TRNEE NOR MYSELF CAUGHT THE ERRONEOUS ALT READBACK. I WAS CHARGED WITH A SYS DEV. PERHAPS THE PLT THOUGHT HE HEARD AN ALT OF 1-1-THOUSAND SINCE THE HDG ISSUED WAS 1-1-0. MAYBE I WOULD HAVE BEEN MORE LIKELY TO CATCH THE ERRONEOUS READBACK ON THE ALT IF I HAD BEEN DIRECTLY COMMUNICATING AND WATCHING THE ACFT RATHER THAN MONITORING MY TRNEE.