What happened
During the landing phase of flight, the crew attempted to lower the landing gear and subsequently received landing gear control and interface unit (LGCIU) fault indications. A visual fly-by performed by another aircraft revealed that the nose wheels were rotated 90 degrees from the required direction for a standard landing.
Despite the incorrect orientation of the nose wheels, the aircraft achieved a normal touchdown. Following the landing, the captain ordered an emergency evacuation using the overwing exits.
The investigation
An examination of the aircraft's steering control valve was conducted to determine the cause of the wheel rotation. Investigators found that the external 'O' rings within the valve had extruded, allowing pressurized hydraulic fluid to bypass the seals and rotate the nose wheels into the incorrect position.
Further investigation revealed that this specific mechanical failure had occurred previously, leading the manufacturer to issue a service bulletin. The operator had not implemented the instructions contained in the service bulletin, though they were not legally required to do so.