Pdx controller described a developing conflict event between a pdx air carrier arrival for runway 28...

Narrative:

A cessna was pointed out to me doing an NDB approach into the troutdale airport. A B737 was on final for 28L and I noticed that they were at the same altitude; both descending; converging as the cessna was north northeast bound to ttd and the B737 was on final. The B737 came over to me and I called traffic right away on the cessna for him to which he reported that he had the cessna in sight. I instructed him to maintain visual separation with the cessna and he replied that he was already instructed to do so and would comply. There was no reason for these two aircraft to get so close. By the time I talked to the B737 there was approximately 1 to 1.5 miles between them at the same altitude and the distance shrunk by the time they passed. Final should have made a bigger hole for the cessna to complete his practice approach into ttd; as well as call me to advise that the B737 had the cessna in sight. This has been an ongoing problem with practice approaches into ttd with finals aircraft into portland.

Original NASA ASRS Text

Title: PDX Controller described a developing conflict event between a PDX Air Carrier arrival for Runway 28L and Cessna conducting a NDB Approach to TTD. The reporter noted the TRACON should have provided more spacing.

Narrative: A Cessna was pointed out to me doing an NDB approach into the Troutdale Airport. A B737 was on final for 28L and I noticed that they were at the same altitude; both descending; converging as the Cessna was north northeast bound to TTD and the B737 was on final. The B737 came over to me and I called traffic right away on the Cessna for him to which he reported that he had the Cessna in sight. I instructed him to maintain visual separation with the Cessna and he replied that he was already instructed to do so and would comply. There was no reason for these two aircraft to get so close. By the time I talked to the B737 there was approximately 1 to 1.5 miles between them at the same altitude and the distance shrunk by the time they passed. Final should have made a bigger hole for the Cessna to complete his practice approach into TTD; as well as call me to advise that the B737 had the Cessna in sight. This has been an ongoing problem with practice approaches into TTD with finals aircraft into Portland.

Data retrieved from NASA's ASRS site as of July 2013 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.

Attributes
ACN	1021037
Time
Date	201207
Local Time Of Day	1801-2400
Place
Locale Reference	PDX.Airport
State Reference	OR
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	Visual Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	Skyhawk 172/Cutlass 172
Flight Phase	Descent
Person 1
Function	Local
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	Conflict Airborne Conflict Deviation - Procedural Published Material / Policy

Pdx controller described a developing conflict event between a pdx air carrier arrival for runway 28L and cessna conducting a NDB approach to ttd. The reporter noted the TRACON should have provided more spacing.