What happened
On May 25, 2018, a Cabri G2 helicopter, registration HB-ZYZ, was conducting a flight training mission departing from Locarno Airport. The flight path took the aircraft through Ascona and up the Maggia Valley toward Bignierte, eventually turning into the Verzasca Valley. While cruising at approximately 3,000 feet AMSL at a speed of 95 knots, the instructor was communicating his position to the Locarno tower via radio.
During this transmission, the instructor observed an object appearing above and to the left of the aircraft, immediately followed by an impact. Although no significant vibrations were felt during the initial cruise, the instructor noted abnormal vibrations during the hover phase prior to landing. Upon inspection after engine shutdown, damage was discovered on a main rotor blade.
The investigation
The investigation established that a drone operator was positioned at the Verzasca dam to photograph the structure. The operator was flying a drone weighing more than 500 grams. While attempting to recover the drone after spotting two other helicopters, the operator lost visual contact and control of the craft. Because the operator was looking south toward the other aircraft, they failed to notice the HB-ZYZ approaching from behind, leading to the collision.
Investigators found that the drone operator was operating within a restricted zone. Specifically, the location was within a prohibited area for drones exceeding 500 grams due to its proximity to Locarno Airport. The investigation also noted that the manufacturer's built-in geofencing limits were less restrictive than the regulations set by the Federal Office of Civil Aviation (FOCA), which allowed the operator to fly the device with only a general warning of a nearby aerodrome.
Findings
- The drone operator utilized a device weighing over 500 grams in a restricted airspace.
- The collision with a drone occurred because the operator's attention was diverted toward other aircraft, leaving the approaching helicopter undetected.
- The main rotor blade sustained two impact marks on the leading edge, resulting in deformation of the lower surface.
- The drone was destroyed in the incident.
Safety action
While the damage to the rotor blade did not necessitate an emergency landing in a hazardous area, the investigation highlighted that a collision with flight controls could have been fatal. The findings emphasize the high risk of drone operations near aerodromes and the potential for even smaller drones (under 500 grams) to cause significant damage to manned aircraft.