Narrative:

Medium large transport X was requesting FL310. Medium large transport X was then turned 15 degrees left and descended to FL310. Then large transport Y at FL330 was turned 15 degrees left pye when able. Medium large transport X didn't start down for 2 mins, however I was going for latitude sep and not vertical. I tried to turn both aircraft another 15 degrees each, but it wasn't enough. The main error here is I gave large transport Y direct pye when able, and he only turned 3-5 degrees at the most, because he was already receiving pye. Callback conversation with reporter revealed the following: reporter was called to ascertain proximity of aircraft, controller's experience level and location or operational error. Reporter stated that his major mistake was in using the phrase, 'direct pye when able.' this caused the large transport to continue toward the medium large transport and thus sep could not be maintained. Another factor which helped the loss of separation was the fact that the medium large transport started down later than the controller anticipated. These 2 elements and the momentary inattn of the controller caused the sep loss.

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Original NASA ASRS Text

Title: LATERAL SEPARATION LOST BETWEEN ACR-LGT AT FL330 AND ACR-MLG DESCENDING FROM FL350 TO FL310.

Narrative: MLG X WAS REQUESTING FL310. MLG X WAS THEN TURNED 15 DEGS LEFT AND DSNDED TO FL310. THEN LGT Y AT FL330 WAS TURNED 15 DEGS LEFT PYE WHEN ABLE. MLG X DIDN'T START DOWN FOR 2 MINS, HOWEVER I WAS GOING FOR LAT SEP AND NOT VERT. I TRIED TO TURN BOTH ACFT ANOTHER 15 DEGS EACH, BUT IT WASN'T ENOUGH. THE MAIN ERROR HERE IS I GAVE LGT Y DIRECT PYE WHEN ABLE, AND HE ONLY TURNED 3-5 DEGS AT THE MOST, BECAUSE HE WAS ALREADY RECEIVING PYE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR WAS CALLED TO ASCERTAIN PROX OF ACFT, CTLR'S EXPERIENCE LEVEL AND LOCATION OR OPERATIONAL ERROR. REPORTER STATED THAT HIS MAJOR MISTAKE WAS IN USING THE PHRASE, 'DIRECT PYE WHEN ABLE.' THIS CAUSED THE LGT TO CONTINUE TOWARD THE MLG AND THUS SEP COULD NOT BE MAINTAINED. ANOTHER FACTOR WHICH HELPED THE LOSS OF SEPARATION WAS THE FACT THAT THE MLG STARTED DOWN LATER THAN THE CTLR ANTICIPATED. THESE 2 ELEMENTS AND THE MOMENTARY INATTN OF THE CTLR CAUSED THE SEP LOSS.

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.