Narrative:

We were metering to msp and issued clearance to hold at dayle intersection to air carrier X and air carrier Y. Tmu rippled the meter list and we noticed that delays were shortened. My trnee issued clearance to air carrier X, who was about 10 mi northwest of dayle outbnd in the holding pattern, to proceed to msp via the arrival, cross exact at or below 15000', descend and maintain 10000'. Since the meter times were such that air carrier X couldn't possibly make it to exact by then, my trnee elected to swap times with air carrier Y who was approaching dayle on his inbound leg. Clearance was issued to air carrier Y to proceed to msp via the arrival, but the aircraft did not answer. Other xmissions were made to other aircraft and another clearance was issued to air carrier Y who was now just past dayle intersection and beginning his turn outbnd. At this point we both felt sure he would stop his right turn and turn back to the left to join the arrival route. He had also been instructed to cross exact intersection at or below 15000', descend and maintain 10000'. His readback of the clearance was 'roger, back to the arrival, cross exact at or below 15000', descend and maintain 10000',' leaving no doubt in our minds that he would turn back to the left to join. Our attention was turned to other duties for a few seconds and then we realized that air carrier Y did not turn left, but instead continued a right turn and was going to conflict with air carrier X, who was now approaching dayle. At this time I observed the altitude readouts of air carrier Y at FL193 and air carrier X at 17800'. I instructed my trnee to stop air carrier Y at FL190, which he did, but the pilot said they were through FL180 and would have to climb back up. My trnee said, 'yes, do that.' at the time the pilot said he was through FL180, I thought I observed the altitude readout at FL187. A left turn was then issued to both aircraft and I to air carrier X to expedite descent. Air carrier Y descended down to 17600' before starting back up and conflicted with air carrier X who was out of 17400'. We assumed what the pilot would do and now realize that we should have instructed air carrier X to make a left turn instead of just saying cleared to msp via the arrs assuming he would turn left.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACR X HAD LESS THAN STANDARD SEPARATION FROM ACR Y. SYSTEM ERROR.

Narrative: WE WERE METERING TO MSP AND ISSUED CLRNC TO HOLD AT DAYLE INTXN TO ACR X AND ACR Y. TMU RIPPLED THE METER LIST AND WE NOTICED THAT DELAYS WERE SHORTENED. MY TRNEE ISSUED CLRNC TO ACR X, WHO WAS ABOUT 10 MI NW OF DAYLE OUTBND IN THE HOLDING PATTERN, TO PROCEED TO MSP VIA THE ARR, CROSS EXACT AT OR BELOW 15000', DSND AND MAINTAIN 10000'. SINCE THE METER TIMES WERE SUCH THAT ACR X COULDN'T POSSIBLY MAKE IT TO EXACT BY THEN, MY TRNEE ELECTED TO SWAP TIMES WITH ACR Y WHO WAS APCHING DAYLE ON HIS INBND LEG. CLRNC WAS ISSUED TO ACR Y TO PROCEED TO MSP VIA THE ARR, BUT THE ACFT DID NOT ANSWER. OTHER XMISSIONS WERE MADE TO OTHER ACFT AND ANOTHER CLRNC WAS ISSUED TO ACR Y WHO WAS NOW JUST PAST DAYLE INTXN AND BEGINNING HIS TURN OUTBND. AT THIS POINT WE BOTH FELT SURE HE WOULD STOP HIS RIGHT TURN AND TURN BACK TO THE LEFT TO JOIN THE ARR RTE. HE HAD ALSO BEEN INSTRUCTED TO CROSS EXACT INTXN AT OR BELOW 15000', DSND AND MAINTAIN 10000'. HIS READBACK OF THE CLRNC WAS 'ROGER, BACK TO THE ARR, CROSS EXACT AT OR BELOW 15000', DSND AND MAINTAIN 10000',' LEAVING NO DOUBT IN OUR MINDS THAT HE WOULD TURN BACK TO THE LEFT TO JOIN. OUR ATTN WAS TURNED TO OTHER DUTIES FOR A FEW SECS AND THEN WE REALIZED THAT ACR Y DID NOT TURN LEFT, BUT INSTEAD CONTINUED A RIGHT TURN AND WAS GOING TO CONFLICT WITH ACR X, WHO WAS NOW APCHING DAYLE. AT THIS TIME I OBSERVED THE ALT READOUTS OF ACR Y AT FL193 AND ACR X AT 17800'. I INSTRUCTED MY TRNEE TO STOP ACR Y AT FL190, WHICH HE DID, BUT THE PLT SAID THEY WERE THROUGH FL180 AND WOULD HAVE TO CLB BACK UP. MY TRNEE SAID, 'YES, DO THAT.' AT THE TIME THE PLT SAID HE WAS THROUGH FL180, I THOUGHT I OBSERVED THE ALT READOUT AT FL187. A LEFT TURN WAS THEN ISSUED TO BOTH ACFT AND I TO ACR X TO EXPEDITE DSNT. ACR Y DSNDED DOWN TO 17600' BEFORE STARTING BACK UP AND CONFLICTED WITH ACR X WHO WAS OUT OF 17400'. WE ASSUMED WHAT THE PLT WOULD DO AND NOW REALIZE THAT WE SHOULD HAVE INSTRUCTED ACR X TO MAKE A LEFT TURN INSTEAD OF JUST SAYING CLRED TO MSP VIA THE ARRS ASSUMING HE WOULD TURN LEFT.

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.