Narrative:

Working finals combined. Staggering the approaches to runway 1C and 1R. The winds at altitude were 10;000 at 10 to 15 knots and the winds below 2;000 were 360 at 08 knots. The winds made it difficult to maintain a staggered approach sequence due to the 1R aircraft being lower first into the headwind and the 1C aircraft being higher with the quartering tail wind. I slowed the dc-9; down to 170; then again to 160 to maintain my stagger with an erj-145 on 1R. The erj-145 slowed to 120 knots ground speed inside the marker. The ARTS will not allow you to put a 2 mile bat up on aircraft until inside the 10 mile range ring in order to use something other than your own vision to gauge a 2 mile stagger between 1C and 1R. When the dc-9 got to the 10 mile range ring; and I was able to put the 2 mile bat up; I was very close to what I need. I took care of a couple other aircraft on frequency; but by the time I got back to the dc-9 just inside the marker; he was not slowing enough so I called the tower and had them break the dc-9 out. They had the dc-9 fly the runway heading. I did anticipate a slower speed on the erj-145; just not down to 120 so soon. I tried to take every action I could without causing the rest of my sector to be affected as well. We had just been instructed to stay off of runway 1R with anymore arrivals for departures. I was trying to adjust speeds on other aircraft to accommodate the switching of their runways and my longer final to 1C. The swirling winds and the tail wind above 2;000 feet and a head wind below 2;000 feet; and the volume of airplanes at the time made it difficult; not too difficult; but added complexity to figuring out just how much room you need to accommodate a stagger. Recommendation; I would like to see the capability of being able to use the ARTS to generate a 2 mile bat on aircraft prior to the 10 mile range ring; for staggering purpose. There are no ARTS aides or tarp to help you indicate when you're about to loose separation when running staggered approaches. Tarp captures things within micro miles. I have human eyes and do the best I can with them; without having to add a large amount of extra room on the final from my feeders to accommodate this unknown wind parameter when it occurs. Winds effect different types of aircraft differently; as well as pilots respond differently. It's only a guess for us. The loss of separation was 1.94 miles for a 2 mile required stagger. I took corrective action two different times to try and mitigate this loss of separation. But I still was unable to do so with only using my eyes; and took the appropriate action when I believed I was unable to maintain an adequate stagger. If the ARTS was allowed to show a 2 mile bat a little sooner for iad; say 15 miles so we could have a better idea of what are stagger was going to look like before we met the LOA requirement of having aircraft switched to iad tower between 12-7 miles; would be very helpful. I will add more separation between my staggers when having these wind situations; and try to be more knowledgeable with the pairing of aircraft on staggered approaches; so as to match up similar type aircraft. I will review all 7110.65 required separation standards. LOA and SOP procedures for handling these situations. Being more vigilant and asking for more room from my feeders during these situations would prove to be helpful as well.

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Original NASA ASRS Text

Title: PCT Controller experienced a loss of separation during staggered approach procedures the reporter commenting on the need for additional spacing tools for controllers if tenths of mile are going to determine a separation loss.

Narrative: Working finals combined. Staggering the approaches to Runway 1C and 1R. The winds at altitude were 10;000 at 10 to 15 knots and the winds below 2;000 were 360 at 08 knots. The winds made it difficult to maintain a staggered approach sequence due to the 1R aircraft being lower first into the headwind and the 1C aircraft being higher with the quartering tail wind. I slowed the DC-9; down to 170; then again to 160 to maintain my stagger with an ERJ-145 on 1R. The ERJ-145 slowed to 120 knots ground speed inside the marker. The ARTS will not allow you to put a 2 mile bat up on aircraft until inside the 10 mile range ring in order to use something other than your own vision to gauge a 2 mile stagger between 1C and 1R. When the DC-9 got to the 10 mile range ring; and I was able to put the 2 mile bat up; I was very close to what I need. I took care of a couple other aircraft on frequency; but by the time I got back to the DC-9 just inside the marker; he was not slowing enough so I called the Tower and had them break the DC-9 out. They had the DC-9 fly the runway heading. I did anticipate a slower speed on the ERJ-145; just not down to 120 so soon. I tried to take every action I could without causing the rest of my sector to be affected as well. We had just been instructed to stay off of Runway 1R with anymore arrivals for departures. I was trying to adjust speeds on other aircraft to accommodate the switching of their runways and my longer final to 1C. The swirling winds and the tail wind above 2;000 feet and a head wind below 2;000 feet; and the volume of airplanes at the time made it difficult; not too difficult; but added complexity to figuring out just how much room you need to accommodate a stagger. Recommendation; I would like to see the capability of being able to use the ARTS to generate a 2 mile bat on aircraft prior to the 10 mile range ring; for staggering purpose. There are no ARTS aides or TARP to help you indicate when you're about to loose separation when running staggered approaches. TARP captures things within micro miles. I have human eyes and do the best I can with them; without having to add a large amount of extra room on the final from my feeders to accommodate this unknown wind parameter when it occurs. Winds effect different types of aircraft differently; as well as pilots respond differently. It's only a guess for us. The loss of separation was 1.94 miles for a 2 mile required stagger. I took corrective action two different times to try and mitigate this loss of separation. But I still was unable to do so with only using my eyes; and took the appropriate action when I believed I was unable to maintain an adequate stagger. If the ARTS was allowed to show a 2 mile bat a little sooner for IAD; say 15 miles so we could have a better idea of what are stagger was going to look like before we met the LOA requirement of having aircraft switched to IAD Tower between 12-7 miles; would be very helpful. I will add more separation between my staggers when having these wind situations; and try to be more knowledgeable with the pairing of aircraft on staggered approaches; so as to match up similar type aircraft. I will review all 7110.65 required separation standards. LOA and SOP procedures for handling these situations. Being more vigilant and asking for more room from my feeders during these situations would prove to be helpful as well.

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.