South African investigators have determined that slippage of a worn nose-gear steering cable led to an Airlink British Aerospace Jetstream 41's veering off the runway during take-off from Port Elizabeth last month.
The aircraft, bound for East London, had travelled around 400m along Port Elizabeth's runway 08 and reached a speed of about 70kt when it started heading to the left. It came off the runway and stopped about 35m from the left-hand edge.
In the early stages of take-off the aircraft is normally steered through a self-centring tiller, which connects to the nose-wheel through a gear and a steering cable.
Once the aircraft reaches about 70kt, the rudder gains sufficient authority to take over from the tiller as the primary steering control.
Inspection of the aircraft, says the South African Civil Aviation Authority, discovered that the steering cable was kinked - possibly during installation - and that it had worn against the steering gear, eventually resulting in intermittent slippage.
The CAA says the maintenance manual specifies that the tiller mechanism and cable is provided as a single unit, but adds: "However, as the vendor for the tiller mechanism is no longer able to provide it as a complete unit, industry practice has become to only replace the cable."
Wear on the gear teeth remains present, it states, and can only be detected once play appears with tiller movement.
None of the 29 passengers and three crew members was injured in the incident, on 18 November, but the event added to concerns over Airlink operations, which had already been under examination following a Jetstream accident in September.
Airlink has since grounded its Jetstream 41 fleet while it addresses a technical issue relating to the type's engines.