Narrative:

Thunderstorms in detroit area had moved to east side of airspace. I was working east departure. Strips were going down the drop tube located about 15 ft behind me at the new departure position (not yet in use). The drop tube at my position was not working. Air carrier X departed dtw on a 180 degree heading climbing to 4000. Tower had appreqed 4000 eastbound on V2 with mtc approach. This is not a normal primary departure route. In fact, at 6000 and above it is a primary arrival route for dtw jets. I got up from my position walked over to the other position as air carrier X was calling me. I observed his target and told him 'radar contact maintain 5000'. Then I got the flight progress strip out of the tube and noticed on the strip that tower had only cleared him to 4000. I turned air carrier Y left to 070 degree. Air carrier Y was inbound from moter intersection to det (detroit city) at 6000. This is known as an m-d aircraft and he was in the normal position on an east heading. I don't know if I told air carrier X to maintain 4000 or not but as air carrier Y was above him I assumed air carrier X was stopping his climb at 4000. I descended air carrier Y to 5000. As air carrier Y descended through 5500 the conflict alert went off between him and air carrier X, who was leaving 4200. I assumed air carrier X's mode C was just off a little and talked to other aircraft. Then I noticed he continued to climb, so I told him to maintain 4000. He told me he had been cleared to 5000. I believe there was divergence when vertical separation was lost.

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Original NASA ASRS Text

Title: ACR WAS DESCENDED TO AN ALT OCCUPIED BY ANOTHER ACFT.

Narrative: TSTMS IN DETROIT AREA HAD MOVED TO EAST SIDE OF AIRSPACE. I WAS WORKING EAST DEP. STRIPS WERE GOING DOWN THE DROP TUBE LOCATED ABOUT 15 FT BEHIND ME AT THE NEW DEP POSITION (NOT YET IN USE). THE DROP TUBE AT MY POSITION WAS NOT WORKING. ACR X DEPARTED DTW ON A 180 DEG HDG CLIMBING TO 4000. TWR HAD APPREQED 4000 EBND ON V2 WITH MTC APCH. THIS IS NOT A NORMAL PRIMARY DEP ROUTE. IN FACT, AT 6000 AND ABOVE IT IS A PRIMARY ARR ROUTE FOR DTW JETS. I GOT UP FROM MY POSITION WALKED OVER TO THE OTHER POSITION AS ACR X WAS CALLING ME. I OBSERVED HIS TARGET AND TOLD HIM 'RADAR CONTACT MAINTAIN 5000'. THEN I GOT THE FLT PROGRESS STRIP OUT OF THE TUBE AND NOTICED ON THE STRIP THAT TWR HAD ONLY CLRED HIM TO 4000. I TURNED ACR Y LEFT TO 070 DEG. ACR Y WAS INBND FROM MOTER INTXN TO DET (DETROIT CITY) AT 6000. THIS IS KNOWN AS AN M-D ACFT AND HE WAS IN THE NORMAL POSITION ON AN EAST HEADING. I DON'T KNOW IF I TOLD ACR X TO MAINTAIN 4000 OR NOT BUT AS ACR Y WAS ABOVE HIM I ASSUMED ACR X WAS STOPPING HIS CLIMB AT 4000. I DESCENDED ACR Y TO 5000. AS ACR Y DESCENDED THROUGH 5500 THE CONFLICT ALERT WENT OFF BETWEEN HIM AND ACR X, WHO WAS LEAVING 4200. I ASSUMED ACR X'S MODE C WAS JUST OFF A LITTLE AND TALKED TO OTHER ACFT. THEN I NOTICED HE CONTINUED TO CLIMB, SO I TOLD HIM TO MAINTAIN 4000. HE TOLD ME HE HAD BEEN CLRED TO 5000. I BELIEVE THERE WAS DIVERGENCE WHEN VERTICAL SEPARATION WAS LOST.

Data retrieved from NASA's ASRS site as of August 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.