Narrative:

I was working the arrival feeder sector. It was busy with WX in the area and strong winds from the southwest. We were supposed to be getting mi in trail from ZLC; over jamnn 20 mi and over spain 12 mi. We were not getting the required spacing from ZLC which required excessive vectoring to achieve spacing to the final controller and the coordination downwind speed of 190 KTS. Air carrier X was on the spain arrival and was vectored off for sequencing. Air carrier Y was on the jamnn arrival supposed to be 20 mi in trail with the aircraft ahead and was only 15 mi in trail. Air carrier Y was slowed on initial contact to 210 KTS and descended to 13000 ft. Air carrier X was being vectored across air carrier Y's flight path and air carrier Y was turned east for additional spacing. Air carrier X was descended; I thought; to 13000 ft and turned north ahead of air carrier Y. I observed air carrier X descending below 13000 ft; the MVA for the area he was at. I asked him to verify altitude and to maintain 13000 ft. He said he was assigned 11000 ft and was climbing back up. I observed the mode C of air carrier X at 12400 ft in the 12600 ft MVA and advised my supervisor of a possible loss of separation. The initial investigation indicates that air carrier X descended to 12200 ft in the 12600 ft MVA and that air carrier Y; a B737; was vectored 4.7 mi being air carrier X; a heavy; and the minimum separation is 5 mi.

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Original NASA ASRS Text

Title: S56 CTLR DESCRIBED OPERROR WHEN SEPARATION WAS LOST BTWN 2 ACFT AND CLRNC FROM TERRAIN WAS LESS THAN REQUIRED.

Narrative: I WAS WORKING THE ARR FEEDER SECTOR. IT WAS BUSY WITH WX IN THE AREA AND STRONG WINDS FROM THE SW. WE WERE SUPPOSED TO BE GETTING MI IN TRAIL FROM ZLC; OVER JAMNN 20 MI AND OVER SPAIN 12 MI. WE WERE NOT GETTING THE REQUIRED SPACING FROM ZLC WHICH REQUIRED EXCESSIVE VECTORING TO ACHIEVE SPACING TO THE FINAL CTLR AND THE COORD DOWNWIND SPD OF 190 KTS. ACR X WAS ON THE SPAIN ARR AND WAS VECTORED OFF FOR SEQUENCING. ACR Y WAS ON THE JAMNN ARR SUPPOSED TO BE 20 MI IN TRAIL WITH THE ACFT AHEAD AND WAS ONLY 15 MI IN TRAIL. ACR Y WAS SLOWED ON INITIAL CONTACT TO 210 KTS AND DSNDED TO 13000 FT. ACR X WAS BEING VECTORED ACROSS ACR Y'S FLT PATH AND ACR Y WAS TURNED E FOR ADDITIONAL SPACING. ACR X WAS DSNDED; I THOUGHT; TO 13000 FT AND TURNED N AHEAD OF ACR Y. I OBSERVED ACR X DSNDING BELOW 13000 FT; THE MVA FOR THE AREA HE WAS AT. I ASKED HIM TO VERIFY ALT AND TO MAINTAIN 13000 FT. HE SAID HE WAS ASSIGNED 11000 FT AND WAS CLBING BACK UP. I OBSERVED THE MODE C OF ACR X AT 12400 FT IN THE 12600 FT MVA AND ADVISED MY SUPVR OF A POSSIBLE LOSS OF SEPARATION. THE INITIAL INVESTIGATION INDICATES THAT ACR X DSNDED TO 12200 FT IN THE 12600 FT MVA AND THAT ACR Y; A B737; WAS VECTORED 4.7 MI BEING ACR X; A HVY; AND THE MINIMUM SEPARATION IS 5 MI.

Data retrieved from NASA's ASRS site as of January 2009 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.