S56 controller experienced loss of separation at 11000 ft with air carrier and C208.

Attributes
ACN	603676
Time
Date	200401
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : slc.airport
State Reference	UT
Altitude	msl bound lower : 11700 msl bound upper : 12000
Environment
Flight Conditions	Mixed
Weather Elements	Snow
Aircraft 1
Controlling Facilities	tracon : s56.tracon
Operator	common carrier : air carrier
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	descent : approach descent : intermediate altitude
Route In Use	arrival : on vectors
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : s56.tracon
Operator	common carrier : air taxi
Make Model Name	Caravan 1 208A
Operating Under FAR Part	Part 135
Flight Phase	descent : approach descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 219 flight time total : 13000 flight time type : 9000
ASRS Report	603676
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 120 flight time total : 6100 flight time type : 3500
ASRS Report	603820
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation
Independent Detector	aircraft equipment : tcas other controllera other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance flight crew : took precautionary avoidance action
Consequence	faa : investigated
Miss Distance	horizontal : 1 vertical : 700
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Descending into slc over ogden VOR on vectors for approach. ATC gave us a descent to 11000 ft MSL from 13000 ft MSL. We were between layers at that time. Out of 12000 ft MSL, received a TA on traffic at 12 O'clock position. I shallowed out descent rate to prevent an RA from happening. We picked up the traffic in enough time (other carrier). We saw he was at 11000 ft MSL heading toward us. (TCASII altitude confirmed this.) I leveled the aircraft at 11700 ft MSL. At that time, ATC gave us 'maintain 12000 ft MSL.' we told him that we had the traffic in sight. We did climb back up to 12000 ft MSL. ATC never issued us the traffic conflict. We never received more than the TA advisory. With the vigilance of both crew members involved, it prevented any further incident. Supplemental information from acn 604109: use strip marking when working out of your normal SOP. I was resequencing aircraft Y opposite direction to the flow when I inadvertently assigned air carrier X the same altitude of aircraft Y C208.

Original NASA ASRS Text

Title: S56 CTLR EXPERIENCED LOSS OF SEPARATION AT 11000 FT WITH ACR AND C208.

Narrative: DSNDING INTO SLC OVER OGDEN VOR ON VECTORS FOR APCH. ATC GAVE US A DSCNT TO 11000 FT MSL FROM 13000 FT MSL. WE WERE BTWN LAYERS AT THAT TIME. OUT OF 12000 FT MSL, RECEIVED A TA ON TFC AT 12 O'CLOCK POS. I SHALLOWED OUT DSCNT RATE TO PREVENT AN RA FROM HAPPENING. WE PICKED UP THE TFC IN ENOUGH TIME (OTHER CARRIER). WE SAW HE WAS AT 11000 FT MSL HEADING TOWARD US. (TCASII ALT CONFIRMED THIS.) I LEVELED THE ACFT AT 11700 FT MSL. AT THAT TIME, ATC GAVE US 'MAINTAIN 12000 FT MSL.' WE TOLD HIM THAT WE HAD THE TFC IN SIGHT. WE DID CLB BACK UP TO 12000 FT MSL. ATC NEVER ISSUED US THE TFC CONFLICT. WE NEVER RECEIVED MORE THAN THE TA ADVISORY. WITH THE VIGILANCE OF BOTH CREW MEMBERS INVOLVED, IT PREVENTED ANY FURTHER INCIDENT. SUPPLEMENTAL INFO FROM ACN 604109: USE STRIP MARKING WHEN WORKING OUT OF YOUR NORMAL SOP. I WAS RESEQUENCING ACFT Y OPPOSITE DIRECTION TO THE FLOW WHEN I INADVERTENTLY ASSIGNED ACR X THE SAME ALT OF ACFT Y C208.

Data retrieved from NASA's ASRS site as of July 2007 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.