MD80 first officer misinterps clearance and turns early while captain was busy programming FMS.

Attributes
ACN	572995
Time
Date	200302
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : stl.airport
State Reference	MO
Altitude	msl single value : 12000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : t75.tracon tower : zzz.tower
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach
Route In Use	arrival star : vandalia 4
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	572995
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	non adherence : clearance other spatial deviation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance flight crew : returned to intended or assigned course
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

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.

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.