Incident Overview
During the landing roll, after the first officer engaged the nose wheel steering, the aircraft made an unexpected left turn. The crew applied right rudder and right brake, but the aircraft exited the runway. The incident occurred on landing runways 17L and 22; the crew had requested runway 35R.
Sequence of Events
Winds were from the south-southwest at 12 knots, gusting to 24 knots. The company computed a 13-knot tailwind, exceeding the company limit of 10 knots. Skid marks on the runway were observed and described as indicating a high rate of speed very late in the landing roll.
Postincident Findings
No previous discrepancies for the nose wheel steering had been noted. During a postincident maintenance taxi check, the aircraft made a left turn that increased its rate rapidly. Maintenance personnel removed and replaced the #4 brake assembly, repaired a shorting wire at the nose wheel steering power lever switch, and replaced the power lever switch. The nose wheel steering actuator was removed and tested; no discrepancies were found.
The director of operations commented that the incident would not have occurred had the aircraft been landed into the wind, and that possible inadvertent disconnection of the steering system was a contributing factor.