Narrative:

While on the RNAV arrival into las; at 12000 ft; a right 60 degree deviation from the arrival route was inadvertently made because of an incorrect FMS input. The aircraft began turning toward the initial arrival fix and off our established routing. This deviation occurred on the 'tyssn one arrival' in between 'cejay' and kaddy' intxns. Once the deviation was noticed; heading mode was selected and the aircraft was turned back on course. The total distance from the arrival procedure at its most was 1.5 mi. Shortly thereafter; ATC instructed us to 'slow to 210 KTS; then descend and maintain 8000 ft; turn right to heading 360 degrees. The aircraft was not commanded to turn until approximately 15 seconds after the assignment. No further deviations occurred.

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Original NASA ASRS Text

Title: DA20 FLT CREW DEVIATES NORTH OF COURSE ON THE TYSSN 1 ARRIVAL INTO LAS AFTER AN INCORRECT FMS INPUT AFTER CEJAY.

Narrative: WHILE ON THE RNAV ARR INTO LAS; AT 12000 FT; A R 60 DEG DEV FROM THE ARR RTE WAS INADVERTENTLY MADE BECAUSE OF AN INCORRECT FMS INPUT. THE ACFT BEGAN TURNING TOWARD THE INITIAL ARR FIX AND OFF OUR ESTABLISHED ROUTING. THIS DEV OCCURRED ON THE 'TYSSN ONE ARR' IN BTWN 'CEJAY' AND KADDY' INTXNS. ONCE THE DEV WAS NOTICED; HDG MODE WAS SELECTED AND THE ACFT WAS TURNED BACK ON COURSE. THE TOTAL DISTANCE FROM THE ARR PROC AT ITS MOST WAS 1.5 MI. SHORTLY THEREAFTER; ATC INSTRUCTED US TO 'SLOW TO 210 KTS; THEN DSND AND MAINTAIN 8000 FT; TURN R TO HDG 360 DEGS. THE ACFT WAS NOT COMMANDED TO TURN UNTIL APPROX 15 SECONDS AFTER THE ASSIGNMENT. NO FURTHER DEVS OCCURRED.

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.