Narrative:

On arrival into stl; we were given direct to the field to maintain 4000. While normally direct is good; direct and high is not. We were told our altitude was for a beech baron crossing in front of us and below. As we got closer; I started to configure as energy management started to become the driving issue. We saw the twin engine pass in front and below us about 500 feet and we were told he was VFR. After passing; we were cleared the visual approach and continued to configure and start our descent towards the field and align ourselves with the runway. As I started to descend I looked out the first officer's window to see the plan form of the twin piston as he was turning into us! We took evasive action and queried approach to see if they were talking to him. They said he was talking to the tower. It's important to note that at this point in my mind there were a couple of things going on. First; I was held high and not on center line so I was working to manage the configuration and energy of the aircraft; thanks to the vectors and restrictions we got. Second; I had a VFR light civil airplane and I didn't have a clue what it was doing and he apparently didn't see us because he was turning right towards us. Third; we were trying to build some sort of mental model that both we and ATC could share about all of this. After two TCAS alerts; some defensive maneuvering on our part; and lots of talking to the tower; it turns out that this dude was on a visual approach for the parallel runway doing a VFR landing. The tower told us that since the runways were close; we would appear close on final. We landed with no incident. A while ago when another carrier was around; we did a lot of lda approaches into stl. It was a common understanding that even if you had been cleared for the visual they wanted you on the lda profile so you didn't get too close to the other aircraft. It was kind of a pain; but the intent was clear. What made both the first officer and I more than a little upset was that we didn't have a clue what the intentions of ATC or this twin piston was up to. Even if we had known; it's generally not a good idea to put a -737 that close to another aircraft without some fairly rock solid understanding about what is expected from everyone. You can keep me high; you can bring me close; but don't keep me high; bring me close; and then present a collision avoidance exercise on me all at the same time.

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Original NASA ASRS Text

Title: Air Carrier on final to STL experienced multiple TCAS alerts with traffic that was not clearly coordinated by ATC; the reporter noting a solid understanding of what was expected of the aircraft involved was absent in this event.

Narrative: On arrival into STL; we were given direct to the field to maintain 4000. While normally direct is good; direct and high is not. We were told our altitude was for a Beech Baron crossing in front of us and below. As we got closer; I started to configure as energy management started to become the driving issue. We saw the twin engine pass in front and below us about 500 feet and we were told he was VFR. After passing; we were cleared the visual approach and continued to configure and start our descent towards the field and align ourselves with the runway. As I started to descend I looked out the First Officer's window to see the plan form of the Twin Piston as he was turning into us! We took evasive action and queried Approach to see if they were talking to him. They said he was talking to the Tower. It's important to note that at this point in my mind there were a couple of things going on. First; I was held high and not on center line so I was working to manage the configuration and energy of the aircraft; thanks to the vectors and restrictions we got. Second; I had a VFR light civil airplane and I didn't have a clue what it was doing and he apparently didn't see us because he was turning right towards us. Third; we were trying to build some sort of mental model that both we and ATC could share about all of this. After two TCAS alerts; some defensive maneuvering on our part; and lots of talking to the Tower; it turns out that this dude was on a visual approach for the parallel runway doing a VFR landing. The Tower told us that since the runways were close; we would appear close on final. We landed with no incident. A while ago when another carrier was around; we did a lot of LDA approaches into STL. It was a common understanding that even if you had been cleared for the visual they wanted you on the LDA profile so you didn't get too close to the other aircraft. It was kind of a pain; but the intent was clear. What made both the First Officer and I more than a little upset was that we didn't have a clue what the intentions of ATC or this Twin Piston was up to. Even if we had known; it's generally not a good idea to put a -737 that close to another aircraft without some fairly rock solid understanding about what is expected from everyone. You can keep me high; you can bring me close; but don't keep me high; bring me close; and then present a collision avoidance exercise on me all at the same time.

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.