What happened
On November 5, 2015, a Jodel DR 1050, registration HB-SEW, was performing training maneuvers at Samedan Airport. Following a series of touch-and-go landings, the aircraft performed a full-stop landing on runway 21. During the landing roll, the aircraft began to drift left of the centerline at a speed of approximately 30 to 40 km/h.
In an attempt to correct the drift, the student pilot applied right rudder. Simultaneously, the instructor applied light pressure to the right toe-brake to assist in the correction. However, the student pilot also applied a significant amount of pressure to the right toe-brake. This simultaneous application of braking force from both seats caused a massive increase in braking effectiveness, triggering the tailwheel lock to disengage. The aircraft then swung violently to the right, rotating approximately 110 degrees. During this rotation, the lateral forces caused the left main landing gear to collapse, resulting in the left wing striking the pavement. There were no injuries to the two occupants.
The investigation
SUST examined the mechanical and operational aspects of the incident. The investigation confirmed that the aircraft's weight and center of gravity were within limits and that there were no pre-existing technical defects. A key technical finding was that a recent modification had replaced the original heel brakes with toe-brakes accessible from both the front left and right seats. Because the braking systems are independent but share a reservoir, simultaneous application of the toe-brakes by both the instructor and the student results in an additive effect, significantly increasing braking force.
Findings
- The primary cause of the accident was a loss of directional control during the landing roll due to excessive braking force.
- The instructor's lack of coordination during the transition of control led to the additive braking effect.
- The instructor's limited experience in the specific role of flight instructor on a tailwheel aircraft demanding for basic training was a contributing factor.
- The instructor failed to use the standard "my controls" call to clearly establish command during the critical phase of the rollout.