P80 TRACON controller reported an arriving aircraft responded to a TCAS RA for a VFR aircraft that h...

Attributes
ACN	1390177
Time
Date	201609
Local Time Of Day	1201-1800
Place
Locale Reference	P80.TRACON
State Reference	OR
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Medium Large Transport
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	STAR TMBRS2
Flight Plan	IFR
Aircraft 2
Make Model Name	Small Aircraft High Wing 1 Eng Fixed Gear
Operating Under FAR Part	Part 91
Flight Phase	Climb
Flight Plan	VFR
Person 1
Function	Approach
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 1
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict

Narrative:

Aircraft X was descending via the tmbrs arrival to pdx. He had been advised of aircraft over mulino (4s9). Aircraft Y was climbing up over the mulino airport. Traffic was exchanged with both aircraft. As aircraft X came closer to the area I advised him once more of the traffic. I also readvised aircraft Y of aircraft X descending for pdx. Aircraft Y advised aircraft X in sight and would maintain visual separation. I then advised aircraft X that the traffic had him in sight and would maintain visual separation. Aircraft X later responded that they were responding to a TCAS RA. They completed the maneuver and then descended without incident to pdx. The location of 4s9 so near to the RNAV arrival is a concern. Although the area is clear of the arrival it is near enough to cause TCAS to alarm. The other option is to remove aircraft from the arrival; causing increased workload to both the pilot and ATC. Perhaps moving the tmbrs arrival slightly west of its present course could mitigate this issue.

Original NASA ASRS Text

Title: P80 TRACON Controller reported an arriving aircraft responded to a TCAS RA for a VFR aircraft that had the arriving aircraft in sight and was maintaining visual separation.

Narrative: Aircraft X was descending via the TMBRS arrival to PDX. He had been advised of aircraft over Mulino (4S9). Aircraft Y was climbing up over the Mulino airport. Traffic was exchanged with both aircraft. As Aircraft X came closer to the area I advised him once more of the traffic. I also readvised Aircraft Y of Aircraft X descending for PDX. Aircraft Y advised Aircraft X in sight and would maintain visual separation. I then advised Aircraft X that the traffic had him in sight and would maintain visual separation. Aircraft X later responded that they were responding to a TCAS RA. They completed the maneuver and then descended without incident to PDX. The location of 4S9 so near to the RNAV arrival is a concern. Although the area is clear of the arrival it is near enough to cause TCAS to alarm. The other option is to remove aircraft from the arrival; causing increased workload to both the pilot and ATC. Perhaps moving the TMBRS arrival slightly west of its present course could mitigate this issue.

Data retrieved from NASA's ASRS site 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.

P80 TRACON controller reported an arriving aircraft responded to a TCAS RA for a VFR aircraft that had the arriving aircraft in sight and was maintaining visual separation.