Incident
On 2 November 2013, a British Aerospace Jetstream 32 airplane, registration ZK-VAH, experienced a loss of directional control during takeoff from Auckland Airport. The airplane began to veer left from the runway centreline. The captain initially corrected the deviation, but at about 90 knots the turn became uncontrollable. The airplane ran off the left side of the runway before the captain could bring it to a stop. No injuries occurred, and there was no damage to the airplane or airport infrastructure.
Investigation
The Transport Accident Investigation Commission (TAIC) investigated the incident. The steering jack and steering selector from the nose wheel steering system were removed and examined at overhaul facilities in the United States. The flight data recorder was downloaded, and the pilots were interviewed. The investigation determined that the uncommanded left turn was caused by a faulty steering selector. However, the defective component within the steering selector could not be determined because of incomplete overhaul records. The isolated nature of the failure and previous actions by the manufacturer led to the conclusion that additional changes to maintenance procedures were not warranted. No recommendations were made.
Flight and Crew Details
The airplane was on a scheduled service to Taupo with 14 passengers. The captain had accrued 5,131 flight hours, including 2,212 on the Jetstream 32. The first officer had 1,250 total hours, with 320 on type. Both pilots reported being well rested and fit to fly. Weather was fine with a light crosswind from the left.
Maintenance History
Two previous defects related to the steering system were reported. In February 2013, a pilot reported a left yaw during takeoff; a cracked nose wheel axle nut and faulty steering jack were replaced. In August 2013, another crew reported a left drift; loose components were addressed and the steering handle replaced, but the problem could not be replicated, and the airplane was returned to service with a request for further reports. No further issues were reported until the incident.
Technical Findings
The steering selector exhibited two faults during functional testing: valve sticking after full left input, allowing continuous fluid flow commanding a left turn, and excessive internal valve leakage. The steering jack showed no anomalies. Hydraulic fluid samples were normal. Flight data showed power was symmetric during acceleration, and the first veer occurred near 70 knots, with a second at 90 knots. The rejected takeoff began at about 100 knots.
Key Lesson
A key lesson identified from the inquiry was that prompt action by a pilot on recognising a loss of directional control during takeoff or landing will minimise the risk of a runway excursion.