Narrative:

While controling the london (loz) lo sector of ZID, an operational error occurred. Aircraft #1, en route from cmh to bna at FL180 and aircraft #2, climbing to 17000 ft, off of lex en route to atl. Aircraft #1 was issued a right turn of 15 degrees (approximately a 210 degree heading), to join the arrival route into bna. Approximately 1 min later, aircraft #2 was turned to a heading of 170 degrees. Having put a polygon (5 mi ring) on aircraft #2 earlier in the situation, I judged that the aircraft, aircraft #2 would remain laterally separated from aircraft #1. After descending aircraft #1 approximately 15 seconds after issuing the 170 degree heading to aircraft #2, I descended aircraft #1 to 15000 ft, and went on and took care of another clearance to another aircraft on the frequency. During issuance of that clearance, aircraft #1 was observed just inside the polygon on aircraft #2. (400 ft and 4 mi at closest point). My observation was that aircraft #2 increased its airspeed after it leveled at 17000 ft and the lateral separation I thought I had insured, was eaten away by the increase in speed by aircraft #2. No further action was taken due to the aircraft diverging by approximately 45 degrees, and there was no further incident. Error detection activated, and I advised my supervisor immediately, that I may have lost standard separation.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACFT #1 DSCNT THROUGH OCCUPIED ALT HAD LTSS FROM ACFT #2. SYS ERROR.

Narrative: WHILE CTLING THE LONDON (LOZ) LO SECTOR OF ZID, AN OPERATIONAL ERROR OCCURRED. ACFT #1, ENRTE FROM CMH TO BNA AT FL180 AND ACFT #2, CLBING TO 17000 FT, OFF OF LEX ENRTE TO ATL. ACFT #1 WAS ISSUED A R TURN OF 15 DEGS (APPROX A 210 DEG HDG), TO JOIN THE ARR RTE INTO BNA. APPROX 1 MIN LATER, ACFT #2 WAS TURNED TO A HDG OF 170 DEGS. HAVING PUT A POLYGON (5 MI RING) ON ACFT #2 EARLIER IN THE SIT, I JUDGED THAT THE ACFT, ACFT #2 WOULD REMAIN LATERALLY SEPARATED FROM ACFT #1. AFTER DSNDING ACFT #1 APPROX 15 SECONDS AFTER ISSUING THE 170 DEG HDG TO ACFT #2, I DSNDED ACFT #1 TO 15000 FT, AND WENT ON AND TOOK CARE OF ANOTHER CLRNC TO ANOTHER ACFT ON THE FREQ. DURING ISSUANCE OF THAT CLRNC, ACFT #1 WAS OBSERVED JUST INSIDE THE POLYGON ON ACFT #2. (400 FT AND 4 MI AT CLOSEST POINT). MY OBSERVATION WAS THAT ACFT #2 INCREASED ITS AIRSPD AFTER IT LEVELED AT 17000 FT AND THE LATERAL SEPARATION I THOUGHT I HAD INSURED, WAS EATEN AWAY BY THE INCREASE IN SPD BY ACFT #2. NO FURTHER ACTION WAS TAKEN DUE TO THE ACFT DIVERGING BY APPROX 45 DEGS, AND THERE WAS NO FURTHER INCIDENT. ERROR DETECTION ACTIVATED, AND I ADVISED MY SUPVR IMMEDIATELY, THAT I MAY HAVE LOST STANDARD SEPARATION.

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.