The nose landing gear of the Airbus A320-200 was jammed, but the tires were perpendicular to the fuselage. How did that happen?
During flight, Brake Steering Control Unit (BSCU) performs1 cyclic tests which slightly rotates NLG from the 0° position. Due to this fatigue, two of the four anti-rotation lugs on the NLG upper support assembly fractured and separated. This allowed NLG to deviate from the 0° position. Another contributing factor was BSCU system logic, which prevented NLG from centering. Also contributing was the lack of a procedure to attempt to reset the BSCU system under these conditions.
This website has some nice pictures of nose landing gear before and after the landing.
A summary of the investigation can be found here.
1: BSCU has other functions too.