Ord controller described a possible loss of in-trail separation between two landing aircraft; noting...

Attributes
ACN	927741
Time
Date	201101
Local Time Of Day	1201-1800
Place
Locale Reference	ORD.Airport
State Reference	IL
Aircraft 1
Make Model Name	B767-200
Operating Under FAR Part	Part 121
Flight Phase	Final Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	Regional Jet CL65 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Final Approach
Flight Plan	IFR
Person 1
Function	Local
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	ATC Issue All Types Deviation - Procedural Published Material / Policy

Narrative:

A heavy B767 was leading and a crj was overtaking the B767. The monitor took action to reduce the crj's speed and called traffic hoping to establish visual separation. I had the j-ball up and was watching this as closely as I could. I didn't observe B767's primary target inside the j-ball but touched it a few times while on final approach. We have had no formal training on the use of the j-ball so I do not know if separation was actually lost. Also with tarp; I can not tell the difference between 4.98 and 5.0. I recommend that ord tower receive training on the use of the j-ball and other devices used to measure distance between aircraft. I also recommend that we be provided in the tower cab at each position the same ability to measure distance in real with the same accuracy as tarp. We are currently being asked to measure with a yard stick but are being double checked with a micrometer.

Original NASA ASRS Text

Title: ORD Controller described a possible loss of in-trail separation between two landing aircraft; noting a lack of training on the J-Ball feature and the difference between TARP equipment and RADAR equipment used in the Tower.

Narrative: A heavy B767 was leading and a CRJ was overtaking the B767. The monitor took action to reduce the CRJ's speed and called traffic hoping to establish visual separation. I had the J-Ball up and was watching this as closely as I could. I didn't observe B767's primary target inside the J-Ball but touched it a few times while on final approach. We have had no formal training on the use of the J-Ball so I do not know if separation was actually lost. Also with TARP; I can not tell the difference between 4.98 and 5.0. I recommend that ORD Tower receive training on the use of the J-Ball and other devices used to measure distance between aircraft. I also recommend that we be provided in the Tower Cab at each position the same ability to measure distance in real with the same accuracy as TARP. We are currently being asked to measure with a yard stick but are being double checked with a micrometer.

Data retrieved from NASA's ASRS site as of April 2012 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.

Ord controller described a possible loss of in-trail separation between two landing aircraft; noting a lack of training on the j-ball feature and the difference between tarp equipment and radar equipment used in the tower.