What happened
On May 12, 2008, an Agusta A109K2 helicopter, registration HB-XWM, operated by Swiss Air Ambulance AG, was engaged in a rescue mission near Brändlen, Switzerland. The crew, including a pilot, a doctor, a crew member, and two rescue specialists, were responding to a report of a paraglider stuck in trees on a steep slope.
During the approach to a suitable landing site located approximately 500 meters from the paraglider, the helicopter struck a wire at an altitude of about 15 meters. The impact severed the wire and caused significant damage to the aircraft's airframe, nose landing gear, and one main rotor blade, while also overloading the main rotor gearbox. Despite the collision, the pilot managed to maintain control and performed a safe landing. There were no injuries among the five occupants.
The investigation
SUST examined the flight path, the technical state of the aircraft, and the regulatory framework regarding obstacle reporting. The investigation established that the pilot was flying a route along the slope to avoid potential obstacles. While the helicopter was equipped with a collision warning system (FLOICE), this system relied on an official database of aeronautical obstacles.
The investigation found that the wire in question did not meet the minimum height requirement of 25 meters for mandatory reporting under Swiss regulations. Consequently, the owner had not reported it, and the obstacle was absent from the official aeronautical database, electronic moving terrain maps, and the pilot's warning systems.
Findings
- The primary cause of the accident was the collision between the helicopter and a wire during the approach to an external landing site.
- The pilot chose a flight path that presented inherent risks by flying close to the terrain/slope.
- The wire was not registered in the official aeronautical obstacle database because it did not reach the mandatory 25-meter height threshold.
- At the time of the accident, the aircraft's weight was approximately 50 kg above the maximum takeoff weight for internal loading.
- The pilot was flying to this specific landing site for the first time.
Safety action
SUST identified a safety deficit regarding obstacles that are dangerous but fall below the mandatory reporting height. To improve safety, the report suggests that the Federal Office of Civil Aviation (FOCA) should consider:
- Simplifying and optimizing the reporting process for all potentially dangerous cables and lines.
- Implementing a general reporting requirement for hazardous wires regardless of height.
- Eliminating reporting fees for owners of such obstacles to encourage more frequent updates.
- Providing clear instructions on official platforms regarding the desirability of reporting non-mandatory but dangerous obstacles.