What happened
On May 27, 2016, a Robin DR 400/140 B, registration HB-KEX, was performing circuit training at Sion Airport (LSGS) under visual flight rules. During the initial landing phase of a touch-and-go sequence, the pilot touched down on runway 25 approximately three to four meters to the left of the runway centerline.
As the aircraft entered the deceleration phase, the pilot attempted to steer the plane back toward the center of the runway while maintaining sufficient airspeed for the subsequent takeoff. However, at a speed of roughly 30 to 35 knots, the aircraft became unstable. To prevent a loss of control and to avoid using the brakes, the pilot elected to reduce engine power to stabilize the aircraft's attitude. Because the aircraft was already positioned toward the left side of the runway where the path was clear, the pilot maintained a straight course. This maneuver resulted in the aircraft exiting the paved surface and coming to a stop in the central grass area.
The investigation
The investigation focused on the sequence of events during the landing and the pilot's decision-making process during the deceleration phase. Investigators examined the aircraft's position on the runway, the speed at which the instability occurred, and the pilot's actions regarding engine power and directional control. The investigation confirmed that while there were no injuries to the pilot or the passenger, the aircraft's path led it off the runway.
Findings
- The primary cause of the excursion was the instability of the aircraft during the low-speed deceleration phase.
- The pilot's decision to cut power was intended to stabilize the aircraft's attitude and avoid the use of brakes.
- The aircraft was already off-center at the time of the power reduction, leading to the excursion into the grass.