What happened
On August 23, 2015, at approximately 11:21 AM, a mid-air collision occurred involving two Ikarus C 42 B ultralight aircraft near Dittingen, Switzerland. The aircraft involved were registered as D-MSON and D-MUHH, part of a three-aircraft formation known as "GrassHoppers." The third aircraft in the formation, D-MHDP, was not involved in the collision.
The formation was performing a choreographed maneuver known as the "Wave." During this sequence, the lead pilot of D-MSON slowed the aircraft to allow the other two pilots to overtake. Following the overtake, the third pilot took the lead, and the lead pilot of D-MSON initiated a series of climbing and descending maneuvers between the paths of the other two aircraft. During a descent phase, the aircraft D-MS and D-MUHH collided. The upper part of D-MSON struck the underside of the rear fuselage of D-MUHH.
Following the impact, D-MUHH entered a vertical dive and crashed into a shed in the village of Dittingen, which was subsequently set on fire by debris. The pilot of D-MUHH was fatally injured. The pilot of D-MSON sustained light injuries and was able to deploy a ballistic parachute system to land safely. The pilot of the third aircraft, D-MHDP, was uninjured.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) reconstructed the flight path using pilot statements, video footage, photographs, and GPS data. The investigation examined the training background of the "GrassHoppers" formation, noting that while the pilots had practiced regularly since 2010, there were no standardized requirements for formation flight training under EASA regulations at the time. The investigation also reviewed the regulatory framework for flight displays in Switzerland, specifically regarding pilot authorizations and the protection of third parties on the ground.
Findings
- The primary cause of the collision was the uncontrolled vertical separation during the "Wave" maneuver, where the lead aircraft's descent brought it into the path of the following aircraft.
- The pilots were performing a complex maneuver involving varying altitudes and speeds, which increased the risk of collision.
- There was a lack of standardized theoretical and practical training or specific certification requirements for performing formation flights under EASA regulations.
- At the time of the accident, Swiss regulations did not explicitly require a formal risk assessment for the protection of third parties located outside the immediate display area.
Safety action
Following the accident, the Swiss Federal Office of Civil Aviation (BAZL) implemented a mandatory risk assessment template for all event organizers in Switzerland. This requires organizers to systematically identify hazards and implement mitigation measures, specifically addressing risks to third parties such as nearby residential areas, roads, and railways.