What happened
On 25 November 2004, a Cessna 550 Citation, registration G-FCDB, was performing a passenger flight from Teesside Airport to Copenhagen. During the takeoff roll on Runway 23, the aircraft experienced a sudden bump and a rightward yaw at approximately 70 knots. The crew reported seeing an animal run toward the aircraft, which they believed caused the disturbance.
In an attempt to correct the yaw, the commander applied rudder, but the aircraft subsequently drifted off the paved surface. The aircraft crossed a grass area and a disused section of Runway 01/19, with the right main wheel tracking through soft ground. The pilot applied differential braking and increased power to the right engine to bring the aircraft back onto the main runway surface. The aircraft eventually taxied back to the apron without any injuries to the two crew members or the single passenger, and no damage was sustained by the aircraft.
The investigation
Investigators analyzed flight data recorder information, which contradicted the crew's perception of a severe heading deviation. While the crew believed a significant swing had occurred, the data showed only minor heading changes. The flight data indicated that the aircraft's accelerations were consistent with traveling over an unprepared surface, but no specific initiating event, such as an animal strike, was detected by the sensors.
An examination of the site revealed tyre marks that indicated the aircraft was not following the runway centerline. Instead, the aircraft was aligned with the runway edge line. The investigation also noted that the area where the aircraft crossed the disused runway lacked specific ground markings to indicate that the dispersal area was not part of the active runway. While the airport provided taxiway lights and reflectors, the lack of centerline markings in the dispersal area contributed to the error.
Findings
- The aircraft was incorrectly lined up on the runway edge line rather than the centerline.
- The perceived sudden yaw was likely caused by the drag of the right main wheel as it encountered the grass and potentially a drain cover at the edge of the disused runway.
- The crew's mental model of the aircraft's position was inaccurate; the rudder input intended to correct a perceived swing actually steered the aircraft toward the runway edge.
- The absence of ground markings in the dispersal area to indicate the boundary of the usable runway contributed to the misalignment.