What happened
On 28 December 2004, a Saab-Scania SF34 toA, registration G-RUNG, arrived at Guernsey Airport on a passenger flight from Jersey. During the landing roll on Runway 27, the commander applied the brakes continuously. This action caused a drop in hydraulic pressure, which subsequently led to a temporary loss of pressure to the nosewheel steering mechanism.
As the aircraft approached taxiway ‘Charlie’ to exit the runway, the pilot attempted to execute a 90-degree turn. However, the steering authority was insufficient to complete the maneuver. Consequently, the right main landing gear drifted onto the grass surface adjacent to the taxiway and sank into the ground before the aircraft came to a complete stop. There were no injuries to the 3 crew members or 7 passengers on board, and the aircraft sustained no damage.
The investigation
Investigators examined the hydraulic and mechanical operation of the nosewheel steering system. The system relies on a single hydraulic actuator and is controlled via a wheel-mounted interface on the left-hand side of the cockpit. For steering to function, the pilot must push the steering wheel down to mechanically engage the system and complete the electrical circuit required to open the steering shutoff valve. The investigation noted that if the nosewheel deflects beyond approximately 15 degrees without the wheel being depressed, the system locks the nosewheel in its current position.
Following the event, the aircraft was inspected by a contracted maintenance organization. The inspection revealed no faults within the aircraft's systems.
Findings
- The loss of steering authority was caused by continuous braking during the landing roll, which reduced hydraulic pressure.
- The reduction in pressure caused a temporary failure of the nosewheel steering functionality.
- The aircraft exited the paved surface because the steering became effective only after the aircraft had already deviated from the taxiway path.