Narrative:

Initially; the denver flow requirement was 5 mit (miles in trail) sayge and 10 mit over landr (normally the requirement is 5 mit sayge and 20 mit landr). This subsequently changed due to the high volume of denver arrivals where tmu told me were at risk of overfeeding denver approach and asked if we could extend the offload mit requirement to 15 mit or 20 mit. I informed the controllers on 35; 16 and 9 that the offload to landr restriction was now 15 mit. I could have split sector 15 off from sector 16 or at the least put a tracker on the 16 position. One reason I did not was that of the controllers available to me. I could also have reemphasized to the 16R controller that offloading denver arrivals to landr was a viable option to alleviate the compression of the arrival stream on the sayge arrival. Right before the error(s) occurred I had received calls from tmu and from the omic that the arrivals were being fed to denver approach too bunched up and they were too high. I told the 16RA controller that the arrivals needed to be taken down or we would run the risk of spinning aircraft. I also told the 16RA controller to ensure that a point out to denver approach was accomplished on air carrier (a) who was nearing the approach boundary and was still above FL190. Air carrier (a) was in front of air carrier (B); air carrier (C) and air carrier (D); in that order. I told the 16RA controller; and not the 16R controller; because I could see the 16R controller was very busy. At this point I could have told the 16R controller to put air carrier (a) over the landr arrival gate. I remained behind the sector position while the error occurred. The error occurred as follows: air carrier (a) had been vectored to the north for his descent and to provide spacing between preceding aircraft. The 16R controller vectored air carrier (B) to the south by 20 degrees for additional spacing. After several moments; air carrier (B) was in or near the lateral confines of denver approach when the 16R controller re-cleared air carrier (B) back to sayge. This resulted in an almost 90 degree turn to the north at which point separation was lost between air carrier (B) and air carrier (C) and then air carrier (B) and air carrier (D). A turn direct denver for air carrier (B) instead of sayge may have prevented the loss of separation. The 16R controller attempted to stop air carrier (D)'s descent at FL200 but the clearance did not come soon enough to prevent a loss in separation. I did not hear the clearance issued to air carrier (B) direct sayge that turned him north into air carrier (C) and air carrier (D). After I had pulled the 16R controller off position; he remarked to me that he should have turned air carrier (B) to direct denver and not direct sayge. Recommendation; I would have had sector 15 decombined from sector 16 sooner or had assigned a third person to sector 16. I should have instructed the 16R controller to offload air carrier (a) to the landr arrival.

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Original NASA ASRS Text

Title: Both a supervisor and controller filed detailed reports regarding a loss of separation event; listing causal and preventative actions that differed; providing diverse perspectives from two different vantage points.

Narrative: Initially; the Denver flow requirement was 5 MIT (Miles In Trail) SAYGE and 10 MIT over LANDR (normally the requirement is 5 MIT SAYGE and 20 MIT LANDR). This subsequently changed due to the high volume of Denver arrivals where TMU told me were at risk of overfeeding Denver Approach and asked if we could extend the offload MIT requirement to 15 MIT or 20 MIT. I informed the controllers on 35; 16 and 9 that the offload to LANDR restriction was now 15 MIT. I could have split sector 15 off from sector 16 or at the least put a tracker on the 16 position. One reason I did not was that of the controllers available to me. I could also have reemphasized to the 16R controller that offloading Denver arrivals to LANDR was a viable option to alleviate the compression of the arrival stream on the SAYGE arrival. Right before the error(s) occurred I had received calls from TMU and from the OMIC that the arrivals were being fed to Denver Approach too bunched up and they were too high. I told the 16RA controller that the arrivals needed to be taken down or we would run the risk of spinning aircraft. I also told the 16RA controller to ensure that a point out to Denver approach was accomplished on Air Carrier (A) who was nearing the approach boundary and was still above FL190. Air Carrier (A) was in front of Air Carrier (B); Air Carrier (C) and Air Carrier (D); in that order. I told the 16RA controller; and not the 16R controller; because I could see the 16R controller was very busy. At this point I could have told the 16R controller to put Air Carrier (A) over the LANDR arrival gate. I remained behind the sector position while the error occurred. The error occurred as follows: Air Carrier (A) had been vectored to the north for his descent and to provide spacing between preceding aircraft. The 16R controller vectored Air Carrier (B) to the south by 20 degrees for additional spacing. After several moments; Air Carrier (B) was in or near the lateral confines of Denver approach when the 16R controller re-cleared Air Carrier (B) back to SAYGE. This resulted in an almost 90 degree turn to the north at which point separation was lost between Air Carrier (B) and Air Carrier (C) and then Air Carrier (B) and Air Carrier (D). A turn direct Denver for Air Carrier (B) instead of SAYGE may have prevented the loss of separation. The 16R controller attempted to stop Air Carrier (D)'s descent at FL200 but the clearance did not come soon enough to prevent a loss in separation. I did not hear the clearance issued to Air Carrier (B) direct SAYGE that turned him north into Air Carrier (C) and Air Carrier (D). After I had pulled the 16R controller off position; he remarked to me that he should have turned Air Carrier (B) to direct Denver and not direct SAYGE. Recommendation; I would have had sector 15 decombined from sector 16 sooner or had assigned a third person to sector 16. I should have instructed the 16R controller to offload Air Carrier (A) to the LANDR arrival.

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.