What happened
On 2 November 2013, a British Aerospace Jetstream 32, registration ZK-VAH, was performing a scheduled flight from Auckland Airport to Taupo with 14 passengers on board. During the takeoff roll on runway 23 Left, the aircraft initially accelerated normally under the control of the captain. However, as the aircraft reached approximately 70 knots, the crew noticed a slight leftward swing.
As the speed increased to 90 knots, the aircraft began an uncontrollable turn to the left. The captain immediately initiated a rejected takeoff, reducing engine power and utilizing a combination of nose wheel steering, asymmetric braking, and asymmetric reverse thrust to maintain the runway centerline. Despite these efforts, the aircraft drifted off the left side of the runway, coming to a stop in the grass approximately 15 metres from the pavement. There were no injuries and no damage to the aircraft or airport infrastructure.
The investigation
Investigators from the Transport Accident Investigation Commission (TAIC) examined the aircraft and its components. The investigation focused on the nose wheel steering system, specifically the steering jack and the steering selector. While initial ground tests of the steering system did not replicate the uncommanded turn, detailed examinations of the steering selector at an overhaul facility in the United States revealed significant internal issues.
Testing showed that after a full left-turn input, the valve would stick, allowing continuous hydraulic fluid flow to the left-turn side of the actuator. This was traced to misadjusted spring boxes within the selector. Because the overhaul records from the facility that previously serviced the component were incomplete, investigators could not determine if the failure was due to worn springs or incorrect adjustments during the last overhaul.
Findings
- The uncommanded left turn during takeoff was caused by a faulty steering selector.
- Incomplete overhaul records prevented investigators from identifying the exact defective sub-component within the selector.
- The failure was considered an isolated incident, as no recent evidence suggested a need for changes to existing maintenance procedures.