What happened
On March 24, 2018, an EC1s35 T1 helicopter, registration HB-ZIR, was engaged in a rescue mission involving an avalanche victim at Col du Grand St-Bernard. After dropping off a mountain guide and a canine handler at a parking area near the hospice, the crew prepared for a return flight to Sion.
At the time of the incident, visibility was poor due to low-lying clouds and a phenomenon known as a Föhn wall, which created diffuse lighting conditions. The wind was recorded at 15 knots with gusts up to 20 knots. To assist with navigation in the low-contrast environment, the pilot selected a nearby traffic sign, located approximately 140 meters away, as a visual reference point.
After performing a hover check to verify technical parameters, the pilot began a slow forward flight toward the chosen reference point. During this phase, the aircraft's altitude decreased toward the snow-covered ground. Although the flight assistant noticed the descending altitude and attempted to warn the pilot, the warning arrived too late. The EC135 T1 collided with the terrain and overturned in the snow. The impact was severe enough to sever the tail boom and destroy three of the four main rotor blades. The two crew members escaped the wreckage without injury.
The investigation
Investigators examined the onboard recording equipment, which tracks engine parameters and error messages. The data analysis revealed no technical anomalies or malfunctions prior to the impact; all systems were operating within normal parameters. The crew also reported no pre-existing technical issues with the aircraft.
Findings
- The pilot was aware of the poor visibility but relied on a single, distant reference point in a landscape with very low contrast.
- The crew failed to recognize the continuous descent of the aircraft toward the ground in a timely manner.
- Gusty tailwinds contributed to a more significant loss of altitude than the crew had anticipated.
- There were no mechanical or technical failures contributing to the accident.