Narrative:

First leg of the day to stl. Talking to stl approach on the TRAKE8 arrival somewhere between kayla arc and foristell; close to foristell. I am the PNF. Cruising at 11000 ft and 250 KTS; approach clears us to descend to 10000 ft and to turn to a heading of 020 degrees when we reach snyder; expect runway 30L. 020 degrees is placed in the heading window by the PF with LNAV still engaged on the arrival. The PF and I had planned for an arrival to runway 30R and had the data already completed in the opc and the FMC loaded with that approach. Upon notification from approach that we can expect 30L; I took out the opc and started to recalculate the landing data and load the FMC. At ftz instead of snyder; the PF selected heading on the autopilot and began the turn to 020 degrees. I do not remember if the PF verbalized this or not. During this turn I was still heads down in the opc and did not realize the aircraft was turning off of the STAR and did not look up to verify where the aircraft was going. In approximately a minute or so; stl approach calls us and asks us where we were going. He told us that we had turned to 020 degree heading at foristell instead of snyder and that he needed us to turn to a heading of 070 degrees. At that point I had realized that the PF had turned early. After responding to the heading change with approach and wings level on a heading of 070 degrees; the PF asked stl approach if we had caused any conflicts with the error and approach responded that with the turn to 070 degrees we avoided anything from happening. ATC did not ask us to call them when we landed. No other issues occurred in flight and the plane was landed safely on 30L. PF and I discussed the event after landing.

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Original NASA ASRS Text

Title: B737 CREW ARRIVING STL ON THE TRAKE8 TURN TO ASSIGNED HDG AT THE WRONG FIX.

Narrative: FIRST LEG OF THE DAY TO STL. TALKING TO STL APPROACH ON THE TRAKE8 ARRIVAL SOMEWHERE BETWEEN KAYLA ARC AND FORISTELL; CLOSE TO FORISTELL. I AM THE PNF. CRUISING AT 11000 FT AND 250 KTS; APPROACH CLEARS US TO DESCEND TO 10000 FT AND TO TURN TO A HEADING OF 020 DEGS WHEN WE REACH SNYDER; EXPECT RUNWAY 30L. 020 DEGS IS PLACED IN THE HEADING WINDOW BY THE PF WITH LNAV STILL ENGAGED ON THE ARRIVAL. THE PF AND I HAD PLANNED FOR AN ARRIVAL TO RUNWAY 30R AND HAD THE DATA ALREADY COMPLETED IN THE OPC AND THE FMC LOADED WITH THAT APPROACH. UPON NOTIFICATION FROM APPROACH THAT WE CAN EXPECT 30L; I TOOK OUT THE OPC AND STARTED TO RECALCULATE THE LANDING DATA AND LOAD THE FMC. AT FTZ INSTEAD OF SNYDER; THE PF SELECTED HEADING ON THE AUTOPILOT AND BEGAN THE TURN TO 020 DEGS. I DO NOT REMEMBER IF THE PF VERBALIZED THIS OR NOT. DURING THIS TURN I WAS STILL HEADS DOWN IN THE OPC AND DID NOT REALIZE THE AIRCRAFT WAS TURNING OFF OF THE STAR AND DID NOT LOOK UP TO VERIFY WHERE THE AIRCRAFT WAS GOING. IN APPROXIMATELY A MINUTE OR SO; STL APPROACH CALLS US AND ASKS US WHERE WE WERE GOING. HE TOLD US THAT WE HAD TURNED TO 020 DEG HEADING AT FORISTELL INSTEAD OF SNYDER AND THAT HE NEEDED US TO TURN TO A HEADING OF 070 DEGS. AT THAT POINT I HAD REALIZED THAT THE PF HAD TURNED EARLY. AFTER RESPONDING TO THE HEADING CHANGE WITH APPROACH AND WINGS LEVEL ON A HEADING OF 070 DEGS; THE PF ASKED STL APPROACH IF WE HAD CAUSED ANY CONFLICTS WITH THE ERROR AND APPROACH RESPONDED THAT WITH THE TURN TO 070 DEGS WE AVOIDED ANYTHING FROM HAPPENING. ATC DID NOT ASK US TO CALL THEM WHEN WE LANDED. NO OTHER ISSUES OCCURRED IN FLIGHT AND THE PLANE WAS LANDED SAFELY ON 30L. PF AND I DISCUSSED THE EVENT AFTER LANDING.

Data retrieved from NASA's ASRS site as of January 2009 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.