C90 controller described a loss of separation event while working aircraft to the final; the reporte...

Narrative:

I was working east arrival vectoring to runway 22R ILS. Air carrier X was established on the 22R ILS; 20 [NM] northeast of ord at 7;000 ft. Air carrier Y was on vectors from sbn 20 [NM] ene at 7;000 ft. Initially [they were] on a 290 heading to go behind air carrier X. Both aircraft were operating at 250 KTS. I had to adjust heading to 310 and then 330 to stay behind air carrier X. I did get visual separation just prior to proximity being less than three miles laterally. Divergence was also in effect as the 310/330 headings were essentially a base leg and air carrier Y was on course to pass behind air carrier X. No conflict alert was activated. I feel the fusion radar presentation threw off my estimation of the closure rate and the converging courses; and it ended up being closer than I would have liked. My perception is that the fusion display appears to jump with regard to the target position; refer to as 'stitching'. I am still getting adjusted to correlating target movement relative to the ground speed read out; especially when vectoring to the final approach course at the speeds we are accustomed to working. I intend to build in a little more 'margin' on headings; spacing and speeds; particularly when vectoring to the final approach course.

Original NASA ASRS Text

Title: C90 Controller described a loss of separation event while working aircraft to the final; the reporter claiming the Fusion Radar contributed to misapplication of separation required.

Narrative: I was working East Arrival vectoring to Runway 22R ILS. Air Carrier X was established on the 22R ILS; 20 [NM] northeast of ORD at 7;000 FT. Air Carrier Y was on vectors from SBN 20 [NM] ENE at 7;000 FT. Initially [they were] on a 290 heading to go behind Air Carrier X. Both aircraft were operating at 250 KTS. I had to adjust heading to 310 and then 330 to stay behind Air Carrier X. I did get Visual Separation just prior to proximity being less than three miles laterally. Divergence was also in effect as the 310/330 headings were essentially a base leg and Air Carrier Y was on course to pass behind Air Carrier X. No Conflict Alert was activated. I feel the Fusion Radar presentation threw off my estimation of the closure rate and the converging courses; and it ended up being closer than I would have liked. My perception is that the Fusion display appears to jump with regard to the target position; refer to as 'stitching'. I am still getting adjusted to correlating target movement relative to the ground speed read out; especially when vectoring to the final approach course at the speeds we are accustomed to working. I intend to build in a little more 'margin' on headings; spacing and speeds; particularly when vectoring to the final approach course.

Data retrieved from NASA's ASRS site as of July 2013 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.

Attributes
ACN	1033392
Time
Date	201208
Local Time Of Day	1801-2400
Place
Locale Reference	ORD.Airport
State Reference	IL
Aircraft 1
Make Model Name	EMB ERJ 145 ER/LR
Operating Under FAR Part	Part 121
Flight Phase	Final Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	EMB ERJ 145 ER/LR
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Departure Approach
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	ATC Issue All Types Deviation - Procedural Published Material / Policy

C90 controller described a loss of separation event while working aircraft to the final; the reporter claiming the fusion radar contributed to misapplication of separation required.