A Boeing 727-51C, 9L-LEK was on route from Cairns to Brisbane, Queensland (Australia), onboard the Captain, Co-pilot (Pilot Flying), Flight-engineer and a maintenance engineer.
9L-LEK, Boeing 727-51C
After an uneventful flight, the descent was started and ATC cleared the flight for an ILS (Instrument Landing System) approach to runway 01 at Brisbane Airport. The wind was easterly gusting at 15 knots, resulting in a crosswind for landing. At 1000 ft altitude the crew became visual with the runway and the remainder of the approach was stabilised and the touchdown, just after 16.00 local time, was normal.
The spoilers and thrust reverser deployed as normal and the aircraft decelerated normally.
At approximately 100 knots (180 km/h) the aircraft started to drift to the right and the co-pilot applied rudder input to correct. As the speed reduced the aerodynamic effectiveness of the rudder reduced, and by 80 knots (145 km/h) full rudder deflection was achieved.
As per standard operating procedure, the co-pilot transferred control to the captain as the aircraft only had a nose wheel steering tiller on the left-hand side of the cockpit. This transfer happened at a speed of approximately 80 knots. During the transfer, the co-pilot informed the captain that he had applied full rudder to keep the aircraft on the centerline. When the captain placed his hand on the nose wheel steering tiller it felt very loose. When he moved the tiller to bring the aircraft back to the runway centreline there was no response from the system and the aircraft continued to veer to the right. DIfferential breaking was used in an attempt to stop the aircraft from leaving the paved surface, but at a speed of approximately 65 knots, the aircraft left the runway. Coming to a stop, undamaged, approximately 40 meters from the runway edge.
The aircraft sitting on the grass (Source atsb.gov.uk)
During the investigation into the incident, it quickly became clear that the nose wheel steering system had failed. It was found that one of the nosewheel steering cables had failed in the forward fuselage area, above the nosewheel, in an area with limited access. The failed cable (a carbon steel cable) was sent for examination by a metallurgical specialist. That examination revealed that 70% of the cable strands at the failure location showed signs of severe aqueous corrosion. (Aqueous corrosion is an electrochemical process by which metals or alloys are oxidised in the presence of solutions containing water. Corrosion rates are significantly affected by environmental conditions such as temperature, humidity, and oxygen availability.)
Example of control cables (generic, not specific to this incident, source public domain)
At the time of the incident, the aircraft had accumulated 54.200 flight hours and 48.000 flight cycles. The maintenance program for the failed cable was based on the condition of the cable. Meaning the cable would only be replaced when the condition of the cable was outside maintenance manual limitations. The same maintenance program called for a visual inspection of the cable during a 'C' check (the last C-check was completed in December 2003)
As a result of this occurrence, the operator advised the investigators that it had replaced both nosewheel steering cables with stainless steel cables. After which the aircraft was released to service. Stainless steel has a higher resistance to corrosion than carbon steel.