What happened
On 22 December 2002, a Boeing 73 and 81Q, registration G-XLAD, was operating a flight from Brussels to Gatwick. During the cruise at FL240, the crew, accompanied by an engineer, noticed the aircraft repeatedly yawing to one side before returning to a normal attitude. These disturbances occurred at irregular intervals, lasting anywhere from 20 seconds to two minutes. The commander noted a tendency for the aircraft to slip to the right, necessitating significant aileron input to maintain a straight track. Crucially, the crew reported that during these events, the rudder pedals became impossible to move, only regaining mobility between the disturbances.
As the aircraft descended toward Gatwick, the severity of the deviations increased. While established on the ILS at FL080, the crew issued a PAN call to Gatwick Approach to report rudder difficulties. During the final approach, the aircraft experienced a significant yaw to the left, requiring full right aileron to compensate. At approximately 300 feet above ground level, the aircraft underwent a pronounced yaw and roll to the right. The aircraft subsequently touched down approximately 30° off the runway centerline, making initial contact on the right main gear. Following the landing, the crew used nosewheel steering to guide the aircraft to a taxiway, where they halted the aircraft and contacted emergency services.
The investigation
Following the incident, the aircraft was removed from service for an extensive inspection involving the operator, maintenance organisations, and Boeing. Engineers examined the pedal mechanisms, rudder cables, and mechanical components at the rear of the aircraft, but found no evidence of restrictions or mechanical faults. Measurements of cable tension and pedal forces were all within established limits. Additionally, the stall management yaw damper units were tested at an overhaul agency and found to be functioning normally.
Analysis of the Flight Data Recorder (FDR) provided a complex picture. While the FDR recorded small, unusual rudder pedal displacements and forces, it did not show the large-amplitude excursions or the extreme control inputs reported by the crew. The manufacturer conducted a study to simulate various scenarios, such as ice build-up, foreign object intrusion, or a "sticky" pedal assembly. While a high-friction scenario in the control circuit forward of the load transducer could partially match the FDR data, the manufacturer noted that such a fault would likely have persisted in subsequent flights, which was not the case.
Findings
- The crew experienced intermittent periods of uncommanded yaw and an inability to manipulate the rudder pedals.
- The investigation was unable to identify a specific mechanical or electrical cause for the reported control difficulties.
- FDR data showed small rudder movements that did not fully align with the more extreme deviations described by the flight crew.
- The aircraft's subsequent operations showed no recurrence of these rudder control issues.