What happened
A Bombardier BD100-1A10 (registration N818RC), operated by Tri Marine Management Company LLC, was landing at Iqaluit airport in Nunavut when it experienced a sudden loss of directional control. The flight, which originated in Long Beach, California, was en route to Italy with a planned fuel stop in the Arctic.
As the aircraft touched down on Runway 3 and the nose wheel made contact with the surface, the aircraft began to veer sharply to the right. The crew attempted to counteract the movement by applying full left rudder, left braking, and using the nose steering tiller, but these inputs were ineffective. The aircraft exited the right side of the runway approximately 4,300 feet from the threshold, traveling 400 feet over frozen ground before coming to a stop in a snow bank. There were no injuries to the two crew members or the single passenger on board, though the aircraft sustained damage to the nose and main landing gear.
The investigation
The investigation focused on why the nose-wheel steering (NWS) failed to respond to pilot inputs and why the aircraft could not revert to a "free castering" mode, which would have allowed for differential braking to maintain the centerline.
Investigators recovered the flight data recorder, which revealed that a master caution warning occurred almost simultaneously with a 16-degree heading change to the right. Analysis of the steering selector valve (SSV) and the electro-hydraulic servo valve (EHSV) showed that the SSV failed to close. This failure prevented the system from entering a bypass mode that would have allowed the nose wheel to steer freely.
Laboratory tests and cold-soak simulations in Iqaluit successfully duplicated the uncommanded right deflection. The investigation also identified hydraulic fluid contamination, including the presence of particles and high water content, which likely contributed to the valve malfunction. Furthermore, the aircraft had been exposed to extreme temperatures of -60°C during its cruise altitude, which may have exacerbated the effects of the contamination.
Findings
- The primary cause of the runway excursion was an uncommanded right turn of the nose-wheel steering upon touchdown.
- The electro-hydraulic servo valve failed to respond to steering commands, and the steering selector valve failed to close, which prevented the crew from using free castering to correct the veer.
- The failure of the servo valve was likely caused by a combination of hydraulic fluid contamination, internal corrosion, and exposure to extreme cold temperatures.
- The investigation noted that the lack of specific inspection requirements or periodic maintenance schedules for these components increases the risk of unexpected failure.