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

Narrative

TFC AND COMPLEXITY WAS HVY AROUND THE ETG AND PSB AREA. MIL RETURNING ACFT AT FL270-290 WBOUND OVER PSB. AT LEAST 4-6 ACFT HAD TO BE MOVED; DSNDED TO INSURE SEPARATION WAS INSURED WITH THE MIL ACFT; THIS TFC SITUATION CAUSED A LOT OF COORD. ACR X WAS DSNDED FROM FL290 TO FL240 TO INSURE SEPARATION WITH SEVERAL ACFT. ACR WAS GIVEN DIRECT TO HDR. ACR Y WAS EBOUND AT FL290 AND DSNDED TO FL250. ACR X WAS LEVEL AT FL240 AND ACR Y WAS LEVEL FL250. ACR Y WAS ISSUED TFC 3 O'CLOCK; 15 MI; NEBOUND AT FL260 AND TOLD TO MAINTAIN FL250. ON THE TAPE ACR Y READ BACK FL230. I THOUGHT I HEARD ACR Y READ BACK FL250. ACR Y WAS SWITCHED TO ZNY FREQ; ACR X WAS ALREADY ON ZNY'S FREQ. THE ACFT HAD ALREADY PASSED WHEN ACR Y DSNDED TO FL230. THE TECHNIQUE OF RESTATING AN ALT TO MAINTAIN WAS DONE TO INSURE THAT SOMETHING LIKE THIS DOESN'T HAPPEN. IN THE FUTURE A COURTESY TA MIGHT NOT BE GIVEN; BUT ONLY IF THE TARGETS ARE GOING TO MERGE. BY TRYING TO BE TOO CONSCIENTIOUS AND DOING MORE WORK THAN NECESSARY MAY HAVE ALLOWED THIS TO HAPPEN. ONLY CORRECTIVE ACTION IS TO TRY AND LISTEN BETTER; AND TRY TO HAVE THE PHRASEOLOGY CHANGED SO THERE ARE NO ALTS GIVEN IN A TA. WORDS TO USE INSTEAD OF THE ALT WOULD BE ABOVE OR BELOW.