S46 controller described TCAS RA event when descending air carrier arrival responded to alert.

Attributes
ACN	787794
Time
Date	200805
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : olm.vortac
State Reference	WA
Altitude	msl single value : 14000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : s46.tracon
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise : level
Flight Plan	VFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller military : 4 controller radar : 19
ASRS Report	787974
Events
Anomaly	conflict : airborne critical
Independent Detector	aircraft equipment : tcas other controllera
Resolutory Action	flight crew : took evasive action
Miss Distance	horizontal : 0 vertical : 500
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft Navigational Facility
Primary Problem	Navigational Facility

Narrative:

Air carrier X observed converging VFR traffic at 13500 ft MSL while descending through 14000 ft MSL. Pilot climbed back up to 14000 ft MSL to avoid collision. VFR traffic was not observed by ATC.

Original NASA ASRS Text

Title: S46 CTLR DESCRIBED TCAS RA EVENT WHEN DESCENDING ACR ARR RESPONDED TO ALERT.

Narrative: ACR X OBSERVED CONVERGING VFR TFC AT 13500 FT MSL WHILE DSNDING THROUGH 14000 FT MSL. PLT CLBED BACK UP TO 14000 FT MSL TO AVOID COLLISION. VFR TFC WAS NOT OBSERVED BY ATC.

Data retrieved from NASA's ASRS site as of May 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.