Narrative:

We were cleared for visual approach to 10R from the south. Around 2500 feet and establishing ourselves on final (slightly south of course) we saw traffic 200 feet above us to the north turning right at us. Tower said it was a VFR caravan; on a downwind for 10L. At 2000 feet he was only 100 feet above us and I could see him descending and turning right into us so I dove down below glide-path. We had flaps 5 and gear down. TCAS kept saying 'traffic'. He was right on top of us and still descending so I sped up and continued descending. I really wanted to go missed; but felt trapped with him on top of me. Tower said he was correcting and was now going to the correct runway. We were below glide slope until 500 feet and didn't get the flaps all in above 1000 feet agl. By 40 feet we were stabilized and fully configured. I called tower and they are filing a report. From their view it looked like he turned right over us and fell behind us. I am certain if I had not taken evasive action we would have collided. We did not get an RA; just a TA and I think it's due to our ground proximity. Portland tower said it was not their fault because the caravan was VFR. He made a big mistake that could've been devastating. The VFR caravan turning into us and poor controlling by control tower. When I called the tower; they said he was right on top of us. Why didn't they correct him sooner?

Related reports:

Google
 

Original NASA ASRS Text

Title: Q400 Captain on an ILS for the right runway experiences a NMAC with a C208 on a visual approach for the left runway. A TCAS TA is annunciated and the Q400 Captain descends visually to avoid the C208.

Narrative: We were cleared for visual approach to 10R from the south. Around 2500 feet and establishing ourselves on final (slightly south of course) we saw traffic 200 feet above us to the north turning right at us. Tower said it was a VFR Caravan; on a downwind for 10L. At 2000 feet he was only 100 feet above us and I could see him descending and turning right into us so I dove down below glide-path. We had flaps 5 and gear down. TCAS kept saying 'traffic'. He was right on top of us and still descending so I sped up and continued descending. I really wanted to go missed; but felt trapped with him on top of me. Tower said he was correcting and was now going to the correct runway. We were below glide slope until 500 feet and didn't get the flaps all in above 1000 feet agl. By 40 feet we were stabilized and fully configured. I called tower and they are filing a report. From their view it looked like he turned right over us and fell behind us. I am certain if I had not taken evasive action we would have collided. We did not get an RA; just a TA and I think it's due to our ground proximity. Portland tower said it was not their fault because the Caravan was VFR. He made a big mistake that could've been devastating. The VFR Caravan turning into us and poor controlling by control tower. When I called the tower; they said he was right on top of us. Why didn't they correct him sooner?

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.