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Summary

Summary

While taxiing for departure, the crew of the Boeing 747 selected the flaps to the take-off position. As the flaps extended, the left outboard aileron deflected to the full down position. The aircraft returned to the gate for rectification.

Investigation revealed that the left aileron cable (AA-11), which connected the inboard aileron quadrant to the aileron cable drum at wing station (WS) 776.98, had failed immediately outboard of the cable drum. The adjacent cable (AB-13), which connected the outboard aileron quadrant to the aileron control drum, was frayed at a location consistent with having been in contact with the other cable. The aileron cable drum had four grooves to accommodate the four separate aileron cables which ran inboard and outboard from the drum and connected to the inboard and outboard aileron quadrants. Markers were installed at the WS767 and WS780 locations to provide visual guidance for the routing and attachment of the aileron cables to specific grooves on the cable drum.

The aileron control drum forward guide pin was bent and displayed evidence of abrasion from interference by the cables. There was also abrasion to the top two grooves of the cable drum. Further examination revealed that the two aileron cable markers (decals) attached to the aileron drum's inboard and outboard mounting brackets at WS767 and WS780 were installed incorrectly. The marker for WS767 was fitted at WS780 and vice versa.

The aircraft had been manufactured in 1983 and had operated 62,399 hours to the time of the incident. Since 2 June 1997, when both cables were changed due to wear, the aircraft had operated 1,022 hours. The appropriate dual certifications, for the aileron control system, had been carried out at that time.

The investigation determined that another aircraft in the operator's fleet had had the same aileron cables changed, due to fraying and wear, about 12 months prior to the incident. This aircraft was inspected and it was found that the aileron cable markers at WS767 and WS780 were also transposed.

The investigation also found that eight other aircraft, from various operators, had aileron cable markers incorrectly installed at the WS767 and WS780 locations. However, it was not possible to determine if the markers had been transposed during, or after, aircraft manufacture.

 
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