What happened
On February 23, 1968, a Bell 47G-2 helicopter, registration HB-XAX, was conducting simulated spraying maneuvers near Bern Airport. The flight, operated by Heliswiss, involved a flight instructor and a student pilot. Instead of using standard spraying equipment, the aircraft was carrying six 20-liter canisters of fuel distributed in the external racks to simulate weight.
During the training session, the instructor attempted to demonstrate how to navigate a corner in an electrical power line. While maneuvering around a bend in the line at an altitude of approximately one meter, the helicopter drifted too close to a row of utility poles. The rotor blades struck a wooden mast belonging to the Belp electricity administration.
The investigation
The investigation examined the mechanical condition of the Bell 47G-2, the weather conditions, and the pilot's performance. Investigators found no evidence of technical malfunctions or mechanical failure in the aircraft or its Lycoming engine. Weather conditions at the time were favorable, with calm winds, good visibility (4500 m), and no solar glare to obstruct the pilot's view.
Findings
- The primary cause of the accident was that the flight instructor maintained an insufficient distance from obstacles while maneuvering near the power lines.
- The collision with the wooden pole caused the rotor blades to shatter and the mast to break.
- The impact forced the rotor shaft and head forward through the cockpit canopy, though it did not strike the occupants.
- There were no injuries to the two crew members, although the aircraft was a total loss.