The aircraft was being operated as a scheduled passenger service from Sydney to Seoul, with the co-pilot as the handling pilot. The crew reported that the pre-departure flight control checks were normal. Shortly after becoming airborne from runway 34L, the co-pilot advised the pilot in command (PIC) that his control wheel had become jammed when attempting to make right wing down aileron inputs. The PIC took control of the aircraft and confirmed that his control wheel also had become jammed. He retained control of the aircraft and the co-pilot advised Air Traffic Services (ATS) that the aircraft was unable to turn to the right. He requested left turns and radar vectors to the south for fuel dumping prior to returning to land. ATS initiated a distress phase. The crew actioned the emergency/abnormal checklist for jammed or restricted flight controls, which includes the statement "use maximum force, including a combined effort by both pilots, if required", but they reported that their attempts made no change to the system. After fuel dumping was completed, the aircraft was vectored, using left turns only, to the runway 34L localiser and configured for the landing. At about 400 ft on final approach, the aileron controls became free and an uneventful landing was carried out.
Inspection by ground engineers determined that a plastic cable guard in the left aileron control cable system had broken. Pieces of shattered plastic were found in the vicinity of the left lower cable pulley system in the vertical cable run behind the cabin sidewall, forward of door 1L. The debris and all the remaining guards were removed from both left and right side vertical cable runs. The lateral control system, including the load limiter system, could not be faulted during full system testing. As there were no replacement cable guards available, the aircraft was approved to return to service with the guards removed.
The lateral controls on the aircraft consist of hydraulically powered inboard and outboard ailerons and flight spoilers on each wing. The controls are connected to the cockpit control wheels by cables, for pilot input. The cable runs are duplicated on each side of the aircraft. The left and right cable runs terminate at quadrants at the bases of the left and right control columns respectively. The control columns are interconnected by a cable loop connected to separate quadrants at the bases of the columns. The right quadrant includes a load limiter which consists of a detent and spring-loaded cam assembly. The load limiter is designed to "break away" under applied force by the crew to enable one control wheel to provide lateral control input should the other side jam for any reason. Roll control is then available, but considerable force is required to overcome the detent cam in the load limiter. Other Boeing aircraft types utilise similar systems.
The aircraft manufacturer issued a Service Letter, 747-SL-27-134, in December 1993, advising that broken cable guards could result in high control wheel forces and suggesting that operators should replace the guards with improved parts when replacement is required. The guards on the right control system on the incident aircraft showed evidence of deterioration, as one guard had been previously repaired with adhesive tape.
The aircraft was leased from an overseas operator. Under the terms of the lease agreement, all major maintenance was conducted by the lessor. The last major maintenance inspection was completed on 25 August 1995. At the time of the incident the aircraft total time in service time was 50,400 hours.
The crew remained at the aircraft whilst the defect was rectified. Both crewmembers remarked that they were surprised at the force required to overcome the load limiter when the system was tested. Though they were aware of the load limiting system from ground training instruction, they had never been physically exposed to the forces required to operate the system.