ACR Y DSCNT THROUGH OCCUPIED ALT HAD LTSS FROM ACR X. SYS ERROR.

Narrative

ACR X WAS NEBOUND ON V162 AT 7000 ENRTE TO EWR. ACR Y WAS SWBOUND ON V162 AT 10000 LNDG AT MDT. MY SECTOR OWNS 9000 FT AND ABOVE; AND HARRISBURG APCH OWNS 8000 FT AND BELOW IN THIS AREA. I CLRED ACR Y TO CROSS THE HWANG INTXN AT 9000 FT. ACR Y READ BACK 'CROSS HWANG AT 7000 FT.' I DID NOT CATCH THE WRONG ALT ON THE READBACK. BEFORE ACR Y EVEN LEFT 10000 FT; I SWITCHED HIM TO HARRISBURG APCH BECAUSE I HAD NO TFC FOR HIM AND NO NEED TO TALK TO HIM ANYMORE. ACR Y THEN DSNDED TO MAKE THE RESTRICTION HE THOUGHT I ISSUED AND SUBSEQUENTLY SEPARATION WAS LOST BTWN ACR Y AND ACR X. THIS INCIDENT OCCURRED AT THE VERY END OF AN 11-7 MIDNIGHT SHIFT AND THOUGH I WORK MANY OF THESE; I GUESS FATIGUE AND COMPLACENCY GOT THE BETTER OF ME. IN THE FUTURE; I WILL BE EXTRA VIGILANT AT THE END OF ALL MY SHIFTS TO ENSURE I DON'T GET STUNG LIKE THIS AGAIN. SUPPLEMENTAL INFO FROM ACN 227918: CRUISING AT 10000 MSL. RECEIVED CLRNC FROM ZNY TO 'CROSS HWANG INTXN AT 7000.' COPLT DID NOT HEAR THIS CLRNC AS HE WAS ON OTHER RADIO GETTING ATIS. CAPT DID HEAR THIS CLRNC AND TOLD COPLT TO READ BACK TO CTR 'CROSS HWANG INTXN AT 7000' WHICH WAS DONE. CTR DID NOT CORRECT THIS READBACK. DSNDED AND CROSSED HWANG AT 7000. LEARNED FROM NEXT CTLR (HARRISBURG APCH CTL) THAT PRIOR CLRNC HAD ACTUALLY BEEN TO CROSS HWANG AT 9000 VS 7000; AND THAT AN 'OPERATIONAL CONFLICT' (UNKNOWN TO US) HAD OCCURRED. I (THE CAPT OF THE FLT) HAD MIS-HEARD OR MISUNDERSTOOD THE CLRNC; BELIEVING IT WAS TO 7000 WHEN; IN FACT; IT HAD BEEN TO 9000. WE READ BACK 7000 AND THE CTR CTLR DID NOT CATCH THE ERROR.