What happened
On the night of December 8, 2000, a Shorts SD3-60, registration OY-MUG, was preparing for takeoff from Ronneby airport in Sweden. The flight was a scheduled service operated by MUK AIR, traveling from Copenhagen to Kalmar. During the takeoff roll on runway 01, the co-pilot noticed that the rudder controls had become unresponsive as the aircraft approached V1 speed. This loss of control caused the aircraft to drift toward the left edge of the runway, striking snow removal markers.
Unable to steer the aircraft back to the center of the runway, the co-pilot applied aft pressure to the control column, causing the aircraft to lift off the ground. The crew maintained a low-altitude flight, parallel to the runway, using the ailerons and elevators to regain directional control. After flying a few hundred meters, the aircraft returned to the runway and came to a stop prior to the threshold following heavy braking. While there were no injuries to the 11 passengers or 3 crew members, the heavy braking caused a tire to deflate, and the aircraft sustained minor damage to runway equipment.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the aircraft's flight control and gust lock systems. The investigation focused on why the rudder became immobile during the high-speed portion of the takeoff roll. Investigators reviewed the design of the electro-mechanical rudder locking system, which utilizes a control lock handle located on a console between the pilot seats.
Technical inspections of the aircraft revealed no mechanical or electrical failures in the rudder lock actuator or the proximity switches. The investigation also considered whether environmental factors, such as de-icing fluid, played a role, but found no evidence to support this. The inquiry focused on the manual operation of the control lock handle and the possibility of human error during the transition of control between the commander and the co-pilot.
Findings
- The rudder became spontaneously locked during the takeoff ground run.
- The control lock handle was likely not fully moved into the correct detent position during the pre-takeoff checks.
- Because the handle is not spring-loaded, vibrations during taxiing could cause the handle to move from a partially unlocked position to a locked position.
- The placement and design of the control lock handle are inadequate, as they allow for such spontaneous locking if not properly secured.
Safety action
Following the incident, the operator updated its pre-takeoff checklist to include a specific verification step: "Control Lock Handle... ckd" to ensure the handle is properly seated in the unlocked position.