ZFW controller described a proximity event after transferring two in trail aircraft to D10; the repo...

Narrative:

Air carrier X and air carrier Y were being sequenced into dal. I let the aircraft compress to about 8 miles and then slowed air carrier Y to 250 KTS behind the air carrier X to get the required spacing. I then switched air carrier X to approach control. I had air carrier Y stopped at [12;000 ft] for additional traffic and told him to reduce speed to 250 KTS; then descend and maintain 10;000 ft to keep him laterally separated just in case the speeds were not compatible with the air carrier X. When I saw air carrier Y leave 12;000 ft; I had 7 miles spacing and told the air carrier Y to cross fingr at 9;000 ft per the letter of agreement with D10. I then switched the air carrier Y to approach and was told after I got off position that I had had a pe. I knew that I had done everything right and was rather upset that they were determining this [to be] a 'deal' since I believe that D10 slowed the air carrier X to 210 KTS to let the two aircraft compress in their airspace. I was told we were not going to call D10 to see if this was the case because it was only a pe. With host not showing immediate and accurate speeds [it] becomes extremely difficult to use spacing when one aircraft is being slowed. If we could get host to better show speeds it would be a great benefit.

Original NASA ASRS Text

Title: ZFW Controller described a proximity event after transferring two in trail aircraft to D10; the reporter indicating compression separations could be better judged with improved HOST speed indications.

Narrative: Air Carrier X and Air Carrier Y were being sequenced into DAL. I let the aircraft compress to about 8 miles and then slowed Air Carrier Y to 250 KTS behind the Air Carrier X to get the required spacing. I then switched Air Carrier X to Approach Control. I had Air Carrier Y stopped at [12;000 FT] for additional traffic and told him to reduce speed to 250 KTS; then descend and maintain 10;000 FT to keep him laterally separated just in case the speeds were not compatible with the Air Carrier X. When I saw Air Carrier Y leave 12;000 FT; I had 7 miles spacing and told the Air Carrier Y to cross FINGR at 9;000 FT per the Letter of Agreement with D10. I then switched the Air Carrier Y to Approach and was told after I got off position that I had had a PE. I knew that I had done everything right and was rather upset that they were determining this [to be] a 'deal' since I believe that D10 slowed the Air Carrier X to 210 KTS to let the two aircraft compress in their airspace. I was told we were not going to call D10 to see if this was the case because it was only a PE. With HOST not showing immediate and accurate speeds [it] becomes extremely difficult to use spacing when one aircraft is being slowed. If we could get HOST to better show speeds it would be a great benefit.

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.

Attributes
ACN	968677
Time
Date	201109
Local Time Of Day	1801-2400
Place
Locale Reference	DAL.Airport
State Reference	TX
Environment
Light	Daylight
Aircraft 1
Make Model Name	Regional Jet CL65 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Aircraft 2
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	ATC Issue All Types Deviation - Procedural Published Material / Policy

ZFW controller described a proximity event after transferring two in trail aircraft to D10; the reporter indicating compression separations could be better judged with improved host speed indications.