Narrative:

Air carrier X lost separation with aircraft Y. At the time I was at the radar associate position at the hlg sector. I received a pointout from pit approach on aircraft Y proceeding southwest between the hlg and mgw boundary at 12000 ft. I tracked a data block on the aircraft and brought it to the attention of the radar controller. The mgw controller then called the radar controller and again pointed out the same aircraft and handed off air carrier X descending to 13000 ft. Several xmissions were made to other aircraft and then air carrier X was cleared to 10000 ft. At this time, I noticed what the controller had done and I tried to take corrective action by placing a distance range indicator around air carrier X and told the radar controller to stop the descent. However, it was too late and air carrier X had already passed through 12200 ft and climbed back to 13000 ft. Supplemental information from acn 257768: originally I had cleared air carrier X to air VOR with holding instructions, pittsburgh approach coordinated for the flight to go past air VOR on a northwest heading and then turn direct to hlg VOR descending to 10000 ft. I issued the clearance in steps. However, I issued the descent clearance in the first step. When I realized that I was not going to have 5 mi with the traffic at 12000 ft, I attempted to reclr air carrier X flight to maintain 13000 ft. I had to wait for aircraft to stop transmitting before I could issue the altitude to air carrier X flight which was now down to 12500 ft descending. It took a short time for air carrier X flight to climb back to 13000 ft.

Related reports:

Google
 

Original NASA ASRS Text

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

Narrative: ACR X LOST SEPARATION WITH ACFT Y. AT THE TIME I WAS AT THE RADAR ASSOCIATE POS AT THE HLG SECTOR. I RECEIVED A POINTOUT FROM PIT APCH ON ACFT Y PROCEEDING SW BTWN THE HLG AND MGW BOUNDARY AT 12000 FT. I TRACKED A DATA BLOCK ON THE ACFT AND BROUGHT IT TO THE ATTN OF THE RADAR CTLR. THE MGW CTLR THEN CALLED THE RADAR CTLR AND AGAIN POINTED OUT THE SAME ACFT AND HANDED OFF ACR X DSNDING TO 13000 FT. SEVERAL XMISSIONS WERE MADE TO OTHER ACFT AND THEN ACR X WAS CLRED TO 10000 FT. AT THIS TIME, I NOTICED WHAT THE CTLR HAD DONE AND I TRIED TO TAKE CORRECTIVE ACTION BY PLACING A DISTANCE RANGE INDICATOR AROUND ACR X AND TOLD THE RADAR CTLR TO STOP THE DSCNT. HOWEVER, IT WAS TOO LATE AND ACR X HAD ALREADY PASSED THROUGH 12200 FT AND CLBED BACK TO 13000 FT. SUPPLEMENTAL INFORMATION FROM ACN 257768: ORIGINALLY I HAD CLRED ACR X TO AIR VOR WITH HOLDING INSTRUCTIONS, PITTSBURGH APCH COORDINATED FOR THE FLT TO GO PAST AIR VOR ON A NW HDG AND THEN TURN DIRECT TO HLG VOR DSNDING TO 10000 FT. I ISSUED THE CLRNC IN STEPS. HOWEVER, I ISSUED THE DSCNT CLRNC IN THE FIRST STEP. WHEN I REALIZED THAT I WAS NOT GOING TO HAVE 5 MI WITH THE TFC AT 12000 FT, I ATTEMPTED TO RECLR ACR X FLT TO MAINTAIN 13000 FT. I HAD TO WAIT FOR ACFT TO STOP XMITTING BEFORE I COULD ISSUE THE ALT TO ACR X FLT WHICH WAS NOW DOWN TO 12500 FT DSNDING. IT TOOK A SHORT TIME FOR ACR X FLT TO CLB BACK TO 13000 FT.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.