A departure controller did not notice that two departures had less than required longitudinal separa...

Narrative:

Dfw was in a south flow departing runways 18L and 17C. Due to weather and ZFW route restrictions; aircraft departing runway 18L were on vectors and the runway 17C departures were still on the RNAV routing. DR1; DR2; and DR3 sectors were all open. I was conducting on the job training (OJT) on DR2.an airbus; departed on the forck SID and was talking with DR1. Approximately 3 miles in trail a CRJ2; departed on the nelyn SID talking to DR2. Both aircraft came off of runway 17C. While my trainee and I were discussing how conventional departures off of dal were drifting into the downwind; we noticed the overtake speeds of the crj-200 indicating 240 knots while airbus was indicating 180 knots.a loss of separation had already occurred. We stopped the crj-200 at 5000 feet and turned them to a 200 heading to reestablish separation. We were also coordinating with DR3 verbally as we were turning into traffic they had off of runway 18L that was on the 190 heading. We had enough lateral separation with DR3 that we were not concerned with our 200 heading. I asked the crj-200 if dfw tower had provided visual separation on departure to see if the coordination was just not passed. The crj-200 said no visual separation was given; but they did have traffic in sight. Once separation was reestablished; we turned and climbed the crj-200 back on course.I wrote up an atsap report about a week or two ago with concerns about this very problem. The RNAV procedures have assigned speeds of 'at or below 240kts.' two aircraft that are on a similar flight path are given 3 miles in trail. The front aircraft decides to go slow; while the trailing aircraft decides to increase to 240 knots. This creates an immediate overtake situation where altitude separation cannot always be ensured. About 10 minutes prior to this situation; DR1 had two mrssh departures that ended up 1 mile in trail. DR1 had to work extra hard to provide ZFW the appropriate 5 mile constant or increasing separation according to our LOA. DR1 was able to maintain altitude separation the entire time. While the RNAV departures work in theory; the speeds need to be changed where the pilots do not have discretion to go any speed they want while a trailing aircraft is overtaking them.

Original NASA ASRS Text

Title: A Departure Controller did not notice that two departures had less than required longitudinal separation due to the unusually slow speed of the first aircraft; an Airbus.

Narrative: DFW was in a south flow departing runways 18L and 17C. Due to weather and ZFW route restrictions; aircraft departing Runway 18L were on vectors and the Runway 17C departures were still on the RNAV routing. DR1; DR2; and DR3 sectors were all open. I was conducting On the Job Training (OJT) on DR2.An Airbus; departed on the FORCK SID and was talking with DR1. Approximately 3 miles in trail a CRJ2; departed on the NELYN SID talking to DR2. Both aircraft came off of Runway 17C. While my trainee and I were discussing how conventional departures off of DAL were drifting into the downwind; we noticed the overtake speeds of the CRJ-200 indicating 240 knots while Airbus was indicating 180 knots.A loss of separation had already occurred. We stopped the CRJ-200 at 5000 feet and turned them to a 200 heading to reestablish separation. We were also coordinating with DR3 verbally as we were turning into traffic they had off of Runway 18L that was on the 190 heading. We had enough lateral separation with DR3 that we were not concerned with our 200 heading. I asked the CRJ-200 if DFW tower had provided visual separation on departure to see if the coordination was just not passed. THE CRJ-200 said no Visual Separation was given; but they did have traffic in sight. Once separation was reestablished; we turned and climbed the CRJ-200 back on course.I wrote up an ATSAP report about a week or two ago with concerns about this very problem. The RNAV procedures have assigned speeds of 'at or below 240kts.' Two aircraft that are on a similar flight path are given 3 miles in trail. The front aircraft decides to go slow; while the trailing aircraft decides to increase to 240 knots. This creates an immediate overtake situation where altitude separation cannot always be ensured. About 10 minutes prior to this situation; DR1 had two MRSSH departures that ended up 1 mile in trail. DR1 had to work extra hard to provide ZFW the appropriate 5 mile constant or increasing separation according to our LOA. DR1 was able to maintain altitude separation the entire time. While the RNAV departures work in theory; the speeds need to be changed where the pilots do not have discretion to go any speed they want while a trailing aircraft is overtaking them.

Data retrieved from NASA's ASRS site 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	1381223
Time
Date	201608
Local Time Of Day	1201-1800
Place
Locale Reference	D10.TRACON
State Reference	TX
Aircraft 1
Make Model Name	Regional Jet 200 ER/LR (CRJ200)
Operating Under FAR Part	Part 121
Flight Phase	Climb
Route In Use	SID NELYN
Flight Plan	IFR
Aircraft 2
Make Model Name	Airbus Industrie Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Climb
Route In Use	SID FORCK
Flight Plan	IFR
Person 1
Function	Departure
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (mon) 6 Air Traffic Control Time Certified In Pos 1 (yrs) 2
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict

A departure controller did not notice that two departures had less than required longitudinal separation due to the unusually slow speed of the first aircraft; an airbus.