What happened
During a scheduled flight from Gällivare to Stockholm, an Airbus A320 (registration not provided) experienced a significant steering malfunction during the takeoff roll on runway 30. The weather conditions were good and the runway surface was dry. As the aircraft began its takeoff roll and the brakes were released, it immediately veered to the left. The pilot attempted to counteract this movement by applying right rudder pedal pressure, but the aircraft continued its leftward trajectory. To prevent further deviation, the pilot decided to abort the takeoff. The aircraft eventually came to a halt with the nose wheel positioned outside the runway boundaries. There were no fatalities or injuries reported during the incident.
The investigation
Investigators focused on recent maintenance activities, noting that a contracted organization had recently replaced the rudder control sensor (RVDT) despite no reported faults in the technical logbook. The crew was also aware that maintenance had been performed on the nose wheel steering system the previous day.
Technical examination of the aircraft revealed that the nose wheel steering responded in the opposite direction of the rudder pedal inputs. The investigation found that a mechanical stop inside the rudder control sensor had broken off. This breakage allowed the sensor shaft to be installed two splines away from the correct rigging position without triggering any system warnings. This misalignment resulted in a reversed electrical output signal, causing the steering to operate in reverse.
Findings
The primary cause of the excursion was the incorrect installation of the nose wheel steering sensor and the failure to perform the required functional test following its installation.
Several contributing factors were identified:
- The maintenance manual failed to provide clear instructions on how to align the sensor shaft during installation or how to verify the sensor's function prior to installation.
- The maintenance manual lacked a detailed description of the necessary alignment procedures relative to the sensor's design and position.
- There were deficiencies in the maintenance organization's routines, specifically regarding the planning and grouping of tasks, which led to the omission of a steering deflection verification during the function test.
- The airworthiness organization's safety management system did not sufficiently focus on identifying operational risks occurring between the airworthiness organization and the maintenance provider.