Narrative:

I was only working 5 aircraft at the time. I issued a descent clearance to aircraft X from FL350 to FL280. The aircraft Y at FL330 was about 20 mi behind and in a sloppy turn to the northeast and appeared to not be a factor with the northbound aircraft X. A couple of mins after issuing the descent clearance, I recalled that the winds were unusually strong and out of the northwest and I figured I may need to re-evaluate the traffic. I ran out the vector lines and knew I wouldn't have 5 mi, so I immediately turned aircraft Y 20 degrees right. As soon as I gave that clearance, I knew that the situation really required an assigned heading (20 degrees right just seems too blase) and one that would more than compensate for the overtake. I chose a 100 degree heading because 1) from their precise position at the time, not accounting for winds, that would put the aircraft Y about 5 mi behind aircraft X's position at present, and 2) taking into account the winds, that heading would likely end up more like a track of 120 degrees, which would be more than enough. However, aircraft Y had the wind at his tail and his turns were sluggish. It was a full min or more before his radar presentation showed even a small change in his track, indicating a turn. This is unusual in that, once a turn is issued to an aircraft, it usually only takes a few hits (30 seconds) before the track shows an obvious change. I should have run out the vector lines before I ever issued the clearance for descent to see whether it was clean or not. But, as I said, traffic was light. On any other day this clearance would've been golden. Instead of opting to use a crutch before I give every clearance, I'd do better to stay aware of all the conditions affecting my sector that day and exercise caution.

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Original NASA ASRS Text

Title: ZOB CTLR MISJUDGES WINDS ALOFT WHEN ISSUING AN F100 VECTORS FOR DSCNT AND THE ACR CONFLICTS WITH AN ENRTE, LEVEL DC9.

Narrative: I WAS ONLY WORKING 5 ACFT AT THE TIME. I ISSUED A DSCNT CLRNC TO ACFT X FROM FL350 TO FL280. THE ACFT Y AT FL330 WAS ABOUT 20 MI BEHIND AND IN A SLOPPY TURN TO THE NE AND APPEARED TO NOT BE A FACTOR WITH THE NBOUND ACFT X. A COUPLE OF MINS AFTER ISSUING THE DSCNT CLRNC, I RECALLED THAT THE WINDS WERE UNUSUALLY STRONG AND OUT OF THE NW AND I FIGURED I MAY NEED TO RE-EVALUATE THE TFC. I RAN OUT THE VECTOR LINES AND KNEW I WOULDN'T HAVE 5 MI, SO I IMMEDIATELY TURNED ACFT Y 20 DEGS R. AS SOON AS I GAVE THAT CLRNC, I KNEW THAT THE SIT REALLY REQUIRED AN ASSIGNED HDG (20 DEGS R JUST SEEMS TOO BLASE) AND ONE THAT WOULD MORE THAN COMPENSATE FOR THE OVERTAKE. I CHOSE A 100 DEG HDG BECAUSE 1) FROM THEIR PRECISE POS AT THE TIME, NOT ACCOUNTING FOR WINDS, THAT WOULD PUT THE ACFT Y ABOUT 5 MI BEHIND ACFT X'S POS AT PRESENT, AND 2) TAKING INTO ACCOUNT THE WINDS, THAT HDG WOULD LIKELY END UP MORE LIKE A TRACK OF 120 DEGS, WHICH WOULD BE MORE THAN ENOUGH. HOWEVER, ACFT Y HAD THE WIND AT HIS TAIL AND HIS TURNS WERE SLUGGISH. IT WAS A FULL MIN OR MORE BEFORE HIS RADAR PRESENTATION SHOWED EVEN A SMALL CHANGE IN HIS TRACK, INDICATING A TURN. THIS IS UNUSUAL IN THAT, ONCE A TURN IS ISSUED TO AN ACFT, IT USUALLY ONLY TAKES A FEW HITS (30 SECONDS) BEFORE THE TRACK SHOWS AN OBVIOUS CHANGE. I SHOULD HAVE RUN OUT THE VECTOR LINES BEFORE I EVER ISSUED THE CLRNC FOR DSCNT TO SEE WHETHER IT WAS CLEAN OR NOT. BUT, AS I SAID, TFC WAS LIGHT. ON ANY OTHER DAY THIS CLRNC WOULD'VE BEEN GOLDEN. INSTEAD OF OPTING TO USE A CRUTCH BEFORE I GIVE EVERY CLRNC, I'D DO BETTER TO STAY AWARE OF ALL THE CONDITIONS AFFECTING MY SECTOR THAT DAY AND EXERCISE CAUTION.

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.