Narrative:

Small transport a departed cid (route of flight, cid-uin-ATLIS5-stl) at FL210. I issued clearance to small transport a to cross atlis intersection at 8000'. Small transport B departed uin (route of flight, uin-ATLIS5-stl) climbing to 8000'. I turned small transport a to a heading of 180 degrees for delay and sequencing to stl. At that time, I thought I had issued small transport a 9000'. Due to the sector complexity and the fact that it was a combined sector at the time, I told the aircraft to maintain 8000 instead of 9000'. We then began the process of decombining the sectors and I issued a turn to small transport a to vector behind small transport B. I had placed 9000' in the data block and wrote 9000' on the flight progress strip. Supplemental information from acn 105150: the controller assigned us 8000' at atlis intersection. We started our descent, reading back the altitude restriction (8000'). About this time our company flight from uin to stl called center off uin. Center assigned them 8000'. A few moments later center called us and re-assigned 8000'. We also read back 8000'. About this time she started vectoring us back and forth across the arrival, due to meter delay. First heading 090 degrees, then 270 degrees, then back to 080. As we established 080 degrees, still descending, a metroliner flew across our 12 O'clock position. I asked the captain to ask center if they had us on radar. 'Verify 9000' was the reply. 'We were assigned 8000',' we replied. 'Turn right to 180 degrees and join for the arrival,' was all that was replied at this time. Factors: we should have questioned the second 8000' assignment, as this is an unusual call, based on my experience with ZKC. The controllers should listen to the readbacks instead of just verifying they received them.

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Original NASA ASRS Text

Title: CTLR ASSIGNED SAME ALT TO 2 ACFT. LESS THAN STANDARD SEPARATION OCCURRED.

Narrative: SMT A DEPARTED CID (ROUTE OF FLT, CID-UIN-ATLIS5-STL) AT FL210. I ISSUED CLRNC TO SMT A TO CROSS ATLIS INTXN AT 8000'. SMT B DEPARTED UIN (ROUTE OF FLT, UIN-ATLIS5-STL) CLBING TO 8000'. I TURNED SMT A TO A HDG OF 180 DEGS FOR DELAY AND SEQUENCING TO STL. AT THAT TIME, I THOUGHT I HAD ISSUED SMT A 9000'. DUE TO THE SECTOR COMPLEXITY AND THE FACT THAT IT WAS A COMBINED SECTOR AT THE TIME, I TOLD THE ACFT TO MAINTAIN 8000 INSTEAD OF 9000'. WE THEN BEGAN THE PROCESS OF DECOMBINING THE SECTORS AND I ISSUED A TURN TO SMT A TO VECTOR BEHIND SMT B. I HAD PLACED 9000' IN THE DATA BLOCK AND WROTE 9000' ON THE FLT PROGRESS STRIP. SUPPLEMENTAL INFO FROM ACN 105150: THE CTLR ASSIGNED US 8000' AT ATLIS INTXN. WE STARTED OUR DSCNT, READING BACK THE ALT RESTRICTION (8000'). ABOUT THIS TIME OUR COMPANY FLT FROM UIN TO STL CALLED CENTER OFF UIN. CENTER ASSIGNED THEM 8000'. A FEW MOMENTS LATER CENTER CALLED US AND RE-ASSIGNED 8000'. WE ALSO READ BACK 8000'. ABOUT THIS TIME SHE STARTED VECTORING US BACK AND FORTH ACROSS THE ARR, DUE TO METER DELAY. FIRST HDG 090 DEGS, THEN 270 DEGS, THEN BACK TO 080. AS WE ESTABLISHED 080 DEGS, STILL DSNDING, A METROLINER FLEW ACROSS OUR 12 O'CLOCK POS. I ASKED THE CAPT TO ASK CENTER IF THEY HAD US ON RADAR. 'VERIFY 9000' WAS THE REPLY. 'WE WERE ASSIGNED 8000',' WE REPLIED. 'TURN RIGHT TO 180 DEGS AND JOIN FOR THE ARR,' WAS ALL THAT WAS REPLIED AT THIS TIME. FACTORS: WE SHOULD HAVE QUESTIONED THE SECOND 8000' ASSIGNMENT, AS THIS IS AN UNUSUAL CALL, BASED ON MY EXPERIENCE WITH ZKC. THE CTLRS SHOULD LISTEN TO THE READBACKS INSTEAD OF JUST VERIFYING THEY RECEIVED THEM.

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.