Narrative:

A DA40 called inbound on the VFR barn transition from the west; a normal routing given to VFR inbound aircraft. Slc was in a south flow. I told the DA40 to maintain 6;000 on initial contact. He was the only airplane inbound to slc anywhere close to towers airspace and on tower's radar display. I got distracted working ground traffic and discussing things with the controller in charge. The DA40 didn't follow the prescribed routing direct to the approach ends of the runways and flew eastbound towards about a 5 mile final north of the airport. Almost simultaneously three events took place. I noticed him off course; the conflict alert warning started going off and approach was calling on the line to see what the DA40 was doing. An A320 was on approximately 6-7 mile final for runway 16L; still talking to the approach controller. I immediately issued an immediate right turn to the DA40 to stay west of the A320 and west of runway 16L final. I had visual separation with both aircraft and also told the DA40 to maintain visual separation which he acknowledged he would do. He turned and stayed west of final for runway 16L. The A320 continued inbound; climbed a little; then approach broke him out; brought him around again and he landed. After talking to the approach controller they issued traffic to the A320; didn't know what the DA40 was doing exactly; and issued a traffic alert with 'suggest you climb'. The A320 climbed per the approach controller's instruction. The A320 also advised he had the other aircraft insight. When the A320 was asked if they wanted to continue the initial approach and land; they requested a 360 to come back around. Instead of the approach controller approving the 360; they just took him out and brought him back around. The DA40 continued his flight south; then over the airport eastbound and transitioned the airspace exiting towers airspace to the north. Recommendation; the VFR transitions that slc [handles] from the west have; for years; caused many aircraft to be in an unsafe proximity to other aircraft on approach to slc. It is not uncommon for a VFR aircraft from the west on the barn transition to end up in the wrong place north of the airport. It probably happens at the very least once every other day. I would eliminate the current VFR transitions slc has for routing VFR aircraft inbound and outbound from/to the west. There have been so many close events with many different circumstances over the years with VFR aircraft on the current transitions. In my opinion they are a dangerous or a precarious operation at times involving IFR aircraft on approach. Usually tower is talking to arrivals farther out on final which would have alerted me to the situation developing sooner. Approach is not required to transfer communications until the final approach fix.

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Original NASA ASRS Text

Title: SLC Controller described a conflict event between a VFR inbound via the 'Barn Transition' and an Air Carrier on final to Runway 16L. The Controller mentioned the Barn VFR arrival procedure frequently causes conflicts.

Narrative: A DA40 called inbound on the VFR Barn Transition from the west; a normal routing given to VFR inbound aircraft. SLC was in a south flow. I told the DA40 to maintain 6;000 on initial contact. He was the only airplane inbound to SLC anywhere close to Towers airspace and on Tower's RADAR display. I got distracted working ground traffic and discussing things with the Controller in Charge. The DA40 didn't follow the prescribed routing direct to the approach ends of the runways and flew eastbound towards about a 5 mile final north of the airport. Almost simultaneously three events took place. I noticed him off course; the Conflict Alert Warning started going off and approach was calling on the line to see what the DA40 was doing. An A320 was on approximately 6-7 mile final for Runway 16L; still talking to the Approach Controller. I immediately issued an immediate right turn to the DA40 to stay west of the A320 and west of Runway 16L final. I had visual separation with both aircraft and also told the DA40 to maintain visual separation which he acknowledged he would do. He turned and stayed west of final for Runway 16L. The A320 continued inbound; climbed a little; then Approach broke him out; brought him around again and he landed. After talking to the Approach Controller they issued traffic to the A320; didn't know what the DA40 was doing exactly; and issued a traffic alert with 'suggest you climb'. The A320 climbed per the Approach Controller's instruction. The A320 also advised he had the other aircraft insight. When the A320 was asked if they wanted to continue the initial approach and land; they requested a 360 to come back around. Instead of the Approach Controller approving the 360; they just took him out and brought him back around. The DA40 continued his flight south; then over the airport eastbound and transitioned the airspace exiting Towers airspace to the north. Recommendation; the VFR transitions that SLC [handles] from the west have; for years; caused many aircraft to be in an unsafe proximity to other aircraft on approach to SLC. It is not uncommon for a VFR aircraft from the west on the Barn Transition to end up in the wrong place north of the airport. It probably happens at the very least once every other day. I would eliminate the current VFR transitions SLC has for routing VFR aircraft inbound and outbound from/to the west. There have been so many close events with many different circumstances over the years with VFR aircraft on the current transitions. In my opinion they are a dangerous or a precarious operation at times involving IFR aircraft on approach. Usually Tower is talking to arrivals farther out on final which would have alerted me to the situation developing sooner. Approach is not required to transfer communications until the final approach fix.

Data retrieved from NASA's ASRS site as of April 2012 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.