Narrative:

Aircraft Y checked in (arrival ric). Aircraft X (ric departure) climbing out. Both aircraft assigned 4000 ft. Course divergence was anticipated. Both aircraft's proximity caused ATC 'collision alarm.' perception of controller was that courses diverged (departure heading 280 degrees; arrival 035 degrees). Pilot of arrival stated traffic in sight and 'passing behind.' investigation discovered loss of separation without proper divergence; at time of 'conflict alert' alarm.

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Original NASA ASRS Text

Title: PCT CTLR EXPERIENCED OPERROR AT 4000 FT WHEN ANTICIPATED COURSE DIVERGENCE FAILED BTWN ARR AND DEP ACFT.

Narrative: ACFT Y CHKED IN (ARR RIC). ACFT X (RIC DEP) CLBING OUT. BOTH ACFT ASSIGNED 4000 FT. COURSE DIVERGENCE WAS ANTICIPATED. BOTH ACFT'S PROX CAUSED ATC 'COLLISION ALARM.' PERCEPTION OF CTLR WAS THAT COURSES DIVERGED (DEP HDG 280 DEGS; ARR 035 DEGS). PLT OF ARR STATED TFC IN SIGHT AND 'PASSING BEHIND.' INVESTIGATION DISCOVERED LOSS OF SEPARATION WITHOUT PROPER DIVERGENCE; AT TIME OF 'CONFLICT ALERT' ALARM.

Data retrieved from NASA's ASRS site as of January 2009 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.