What happened
On August 1, 2019, at 18:39 local time, an Airbus Helicopters MBB-BK 117 D-2, registration HB-ZQM, was conducting a medical emergency flight from the REGA base in St. Gallen to Walzenhausen. The crew, consisting of a pilot, a physician, and a paramedic, was utilizing onboard navigation tools and an Electronic Flight Bag to identify obstacles at the landing site. During the initial approach to a roadside location, the rotor downwash dislodged a lid from a nearby grit container, prompting the pilot to abort the landing and hover at a safe distance until the ground crew secured the lid.
Seeking an alternative landing spot, the pilot attempted a second approach at a nearby road curve. During this maneuver, a main rotor blade struck a telephone cable spanning the area, severing the line. The pilot and physician both observed the cable at the moment of impact. Following the strike, the pilot experienced no vibrations or loss of control and successfully diverted to an open landing area approximately 1.4 km away to land safely.
The investigation
Technical inspections of the HB-ZQM revealed rubber residue from the cable on the outer edge of a main rotor blade, but no structural damage was found on the aircraft. The investigation established that while the crew had identified the presence of low-altitude wires via their digital databases, the pilot had misjudged the specific path of the cable during the second approach. The investigation also noted that the sun's position, low in the sky and ahead of the aircraft, may have caused glare, further obscuring the thin wires.
Findings
- The pilot incorrectly assessed the trajectory of the telephone line, believing it spanned a different area of the meadow.
- Sun glare likely contributed to the difficulty in detecting the thin cable.
- Low-altitude obstacles such as telephone lines and hay cables, which often sit below 25 meters, are not included in standard official aviation databases, though they were visible on the operator's enhanced digital maps.
- The incident resulted in no injuries to the crew or third parties, though the telephone cable was severed.