Narrative:

I was the radar controller. Dfw approach had turned the terminal area/dfw airport to a north flow. First; we went into holding. Then; holding established; the hand off moved to the d-side. We were told to move some aircraft into low altitude to hold closer to approach. The metering list (very rarely used) came up; but we were told to ignore it. As we were clearing aircraft into the low altitude sector; we were told to clear them in; 10 mit; 250 KTS. We started doing that. Low was informed; but we were not; that even thought the airport was north; the south flow restrictions were in use (much more restrictive over our corner post). Low contacted us; and we began forcing aircraft down to help with those restrictions. We were then told to move from in-trail to using the metering times. Due to all aircraft being on vectors at this point; we had no easy opportunity to transition to holding for the about 8 minute delays; leading to very large s-turns for all dfw arrival aircraft. We then had two overflights in the opposite direction of flow; one at FL250 needing to get into low who wanted to cross the dfw traffic corridor for weather; one higher who just needed watching. Several point outs from the departure sectors on both sides. The aircraft needing to get into low took much communication and coordination time; particularly for the d-side. Two aircraft on the southern transition; landing west side (northern part of the gate); both were issued non discretionary descents; later both were told to expedite the descent (with the intent of getting the below the dfw traffic; then turning them north to get on the correct transition side). An E135 was the second of these and did not match the performance or descent rate of the first aircraft; which leveled at FL240 further back. The MD82 was stepped down with other dfw traffic to keep speed consistent; on an south vector; due to turn in shortly. After dealing with other portions of the sector; I looked back to check the progress of the E135; and had to move data blocks to see the traffic. I then saw the confliction about 20 seconds before separation was lost. Vertical was already lost; so I turned each aircraft 40 degrees left; and began descending the MD82. Once the aircraft were separated; I put the E135 back on his vector; switched him to low altitude; turned the MD82 back in to the corner post; and gave him to low altitude; then continued sequencing the arrivals. The unaccustomed metering; the confusion about entering metering; the counter-flow lander requiring much coordination; the weather; and the odd restrictions from approach control all altered the normal flow of sequencing in the sector. Normally; west satellite arrivals in a north flow would never have been a factor for dfw arrivals; as the dfw traffic would not need to have been forced down. Recommendation; metering; we should enter and use metering; or we should use in-trail spacing. Trying to transition from one to the other; particularly when coming out of holding; caused the sequence to start off ugly. Metering itself is used far too infrequently since the traffic declines. The overflight at FL250 should have been forced around the arrival corner post; not over it. This is a black mark against both the sector team I was part of; and the one who gave us the aircraft heading direct into an arrival push and weather. Getting into holding is considered a major hazard; requiring a hand off; but metering and coming out of holding are not. This should be re-examined by management.

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Original NASA ASRS Text

Title: ZFW Controller described a loss of separation event during confused and unaccustomed metering procedures; holding and counter-flow traffic also contributed to the event.

Narrative: I was the RADAR Controller. DFW Approach had turned the terminal Area/DFW Airport to a North Flow. First; we went into holding. Then; holding established; the hand off moved to the D-Side. We were told to move some aircraft into low altitude to hold closer to approach. The metering list (VERY rarely used) came up; but we were told to ignore it. As we were clearing aircraft into the low altitude sector; we were told to clear them in; 10 MIT; 250 KTS. We started doing that. Low was informed; but we were not; that even thought the airport was north; the south flow restrictions were in use (much more restrictive over our corner post). Low contacted us; and we began forcing aircraft down to help with those restrictions. We were then told to move from in-trail to using the metering times. Due to all aircraft being on vectors at this point; we had no easy opportunity to transition to holding for the about 8 minute delays; leading to very large S-turns for all DFW arrival aircraft. We then had two overflights in the opposite direction of flow; one at FL250 needing to get into low who wanted to cross the DFW traffic corridor for weather; one higher who just needed watching. Several point outs from the departure sectors on both sides. The aircraft needing to get into low took much communication and coordination time; particularly for the D-Side. Two aircraft on the southern transition; landing west side (northern part of the gate); both were issued non discretionary descents; later both were told to expedite the descent (with the intent of getting the below the DFW traffic; then turning them north to get on the correct transition side). An E135 was the second of these and did not match the performance or descent rate of the first aircraft; which leveled at FL240 further back. The MD82 was stepped down with other DFW traffic to keep speed consistent; on an S vector; due to turn in shortly. After dealing with other portions of the sector; I looked back to check the progress of the E135; and had to move data blocks to see the traffic. I then saw the confliction about 20 seconds before separation was lost. Vertical was already lost; so I turned each aircraft 40 degrees left; and began descending the MD82. Once the aircraft were separated; I put the E135 back on his vector; switched him to low altitude; turned the MD82 back in to the corner post; and gave him to low altitude; then continued sequencing the arrivals. The unaccustomed metering; the confusion about ENTERING metering; the counter-flow lander requiring much coordination; the weather; and the odd restrictions from Approach Control all altered the normal flow of sequencing in the sector. Normally; west satellite arrivals in a north flow would never have been a factor for DFW arrivals; as the DFW traffic would not need to have been forced down. Recommendation; metering; we should enter and use metering; or we should use in-trail spacing. Trying to transition from one to the other; PARTICULARLY when coming out of holding; caused the sequence to start off ugly. Metering itself is used far too infrequently since the traffic declines. The overflight at FL250 should have been forced around the arrival corner post; not over it. This is a black mark against both the sector team I was part of; and the one who gave us the aircraft heading direct into an arrival push and weather. Getting into holding is considered a major hazard; requiring a hand off; but metering and coming out of holding are not. This should be re-examined by management.

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.