Circumstances
On 1 December 2008, employees of a company specializing in challenging tree removal operations prepared for a transport assignment along the Aare riverbank in Bern, Switzerland. The task involved removing individual trees, requiring approximately 120 rotations. In this type of operation, a climbing specialist ascends the tree, secures it with climbing gear, and uses a chainsaw. The helicopter hovers over the tree, and attachment cables are connected to the longline hook. The climbing specialist then cuts the section of the tree that is connected to the helicopter via the cables. The helicopter lifts the cut section and transports it to a drop-off point.
Flight Sequence
On the day before the accident, the climbing specialist prepared a tree with three branches forming the crown. He attached wire cables to two of the three branches, believing this would be sufficient to lift the entire crown section. On the evening of 1 December, the helicopter, a Kaman K-1200 registered as HB-ZGK, was flown to Bern for the upcoming transport flights.
On the morning of 2 December 2008, the pilot conducted several transport flights as described. Around 10:00 LT, the team attempted to remove the tree with the three-branch crown. The climbing specialist climbed to a height of about 5–6 meters and connected the two wire cables to the helicopter's hook. As the pilot increased tension by slightly raising the helicopter, the climbing specialist began cutting the crown section with a chainsaw. A ground helper monitored the operation, and all personnel had radio contact.
After cutting through the trunk, the helicopter lifted the crown. When it was about 2–3 meters high, the load tilted horizontally. The third branch, which had not been secured, broke off. This branch, approximately 16 meters long and weighing about 450 kg, fell along the remaining trunk and struck the climbing specialist, causing serious injuries. The specialist remained secured by his climbing gear and briefly lost consciousness. Two other climbing specialists rescued the injured worker, and a paramedic present at the worksite provided initial medical care. The helicopter continued to the drop-off point with the remaining attached load.
Meteorological Conditions
MeteoSwiss provided the following weather data for the accident time and location: clouds 1/8 at 2000 ft AMSL and 6-7/8 at 5500 ft AMSL, damp haze, visibility around 10 km, wind variable 2-4 kt, temperature 3°C, dew point -1°C, QNH 1010 hPa at LSZB, 1010 hPa at LSZH, 1011 hPa at LSGG, sun azimuth 147° and elevation 14°. No hazards were identified.
Aircraft Information
The Kaman K-1200 is a single-seat transport helicopter powered by a turbine, equipped with two intermeshing counter-rotating rotors. This design eliminates the need for a tail rotor and reduces downwash. The HB-ZGK was fitted with a 50-meter longline with an electrically operated cargo hook at the end.
Findings
The investigation found no pre-existing technical defects on the helicopter or transport equipment. The pilot held the required licenses, and no health issues were identified. The climbing specialist had extensive experience in tree removal with helicopters, having prepared trees for about 5,000 rotations since 1995. The transport operation was thoroughly planned. The helicopter's mass and center of gravity were within limits. The weather did not influence the accident. The climbing specialist himself prepared the tree crown by attaching wire cables to only two of the three branches. After lifting, the unsecured branch broke off and seriously injured the specialist.
Cause
The accident occurred because, while lifting a tree section as an external load, a branch broke off and fell, injuring a member of the forestry team, due to the load not being properly secured.