Narrative:

On vandalia 4 arrival into stl, proceeding direct to the P intersection and descending to 7000 ft MSL, captain/PNF received clearance from stl approach control to depart south intersection on a heading of 290 degrees. First officer/PF heard only the captain read back the clearance to ATC -- first officer/PF understood the clearance to be 'turn right to 290 degrees and then proceed to south intersection.' first officer/PF turned immediately to the new heading of 290 degrees/heading select mode, while continuing the descent to 7000 ft. Prior to the heading change, the aircraft was in the navigation track mode direct to the P intersection. During the turn to 290 degrees, the captain/PNF was loading the correct clearance into the FMS and did not notice that the first officer/PF had selected the new heading manually. The captain/PNF felt the aircraft in the r-hand turn, but understood this to be the aircraft intercepting the outbound radial from vandalia VOR/P intersection to south intersection. The turn put the aircraft north of this outbound radial, 250 degree radial. After a few mins, stl approach control asked us to turn direct stl VOR. I do not believe any loss of separation occurred during this deviation premature turn.

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Original NASA ASRS Text

Title: MD80 FO MISINTERPS CLRNC AND TURNS EARLY WHILE CAPT WAS BUSY PROGRAMMING FMS.

Narrative: ON VANDALIA 4 ARR INTO STL, PROCEEDING DIRECT TO THE P INTXN AND DSNDING TO 7000 FT MSL, CAPT/PNF RECEIVED CLRNC FROM STL APCH CTL TO DEPART S INTXN ON A HDG OF 290 DEGS. FO/PF HEARD ONLY THE CAPT READ BACK THE CLRNC TO ATC -- FO/PF UNDERSTOOD THE CLRNC TO BE 'TURN R TO 290 DEGS AND THEN PROCEED TO S INTXN.' FO/PF TURNED IMMEDIATELY TO THE NEW HDG OF 290 DEGS/HDG SELECT MODE, WHILE CONTINUING THE DSCNT TO 7000 FT. PRIOR TO THE HDG CHANGE, THE ACFT WAS IN THE NAV TRACK MODE DIRECT TO THE P INTXN. DURING THE TURN TO 290 DEGS, THE CAPT/PNF WAS LOADING THE CORRECT CLRNC INTO THE FMS AND DID NOT NOTICE THAT THE FO/PF HAD SELECTED THE NEW HDG MANUALLY. THE CAPT/PNF FELT THE ACFT IN THE R-HAND TURN, BUT UNDERSTOOD THIS TO BE THE ACFT INTERCEPTING THE OUTBOUND RADIAL FROM VANDALIA VOR/P INTXN TO S INTXN. THE TURN PUT THE ACFT N OF THIS OUTBOUND RADIAL, 250 DEG RADIAL. AFTER A FEW MINS, STL APCH CTL ASKED US TO TURN DIRECT STL VOR. I DO NOT BELIEVE ANY LOSS OF SEPARATION OCCURRED DURING THIS DEV PREMATURE TURN.

Data retrieved from NASA's ASRS site as of July 2007 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.