What happened
On 27 February 1998, a Saab-Scania SF340B, registration G-GNTH, was performing a scheduled passenger flight to Glasgow when it veered off the runway at Leeds Bradford Airport. During the takeoff roll, the aircraft initially drifted to the left of the centerline before swinging sharply to the right. Despite the commander applying significant left rudder and attempting to use nosewheel steering, the aircraft could not be maintained on the runway.
As the aircraft accelerated, the crew experienced lateral oscillations. At an airspeed of approximately 96 kt, the commander closed the power levers and applied braking. The aircraft left the paved surface at the intersection 'Delta', traveling onto the grass and eventually coming to a halt approximately 500 yards from the runway. There were no fatalities and no injuries among the 15 passengers or 3 crew members on board. The aircraft sustained minor damage to the brakes, wheels, and rudder stops.
The investigation
Investigators examined the aircraft's flight data recorder (FDR) and runway markings. The tyre marks indicated that while the aircraft was tracking right, it was still heading relatively straight down the runway, suggesting large lateral forces were acting upon it. The FDR showed that the engines were operating symmetrically and that the first officer was correctly maintaining aileron deflection into the wind.
Technical analysis focused on the nosewheel steering system. While the system appeared functional during later tests, investigators noted that the nosewheel marks suggested the wheels were not free to align with the direction of travel. A subsequent, similar incident involving the same aircraft at a different airport suggested that an intermittent fault in the steering mechanism might cause the steering brake to remain engaged, potentially locking the nosewheel at an angle.
Findings
- The aircraft was subjected to strong wind gusts that likely exceeded the operator's maximum permitted crosswind component of 35 kt.
- Initial rudder inputs by the commander were inappropriate for the wind conditions, contributing to the initial deviation.
- A potential malfunction in the nosewheel steering mechanism may have caused the nosewheel to lock at an angle, creating a powerful yawing moment to the right.
- The short timeframe between the onset of the deviation and the aircraft leaving the runway left the commander with very little time to implement corrective actions.