What happened
On 7 July 2004, a Bell 206 helicopter, registration SE-HLK, was performing a routine commercial transport mission in the Tärnafjällen mountains of Sweden. The flight involved transporting three service technicians and equipment to a radio station located in a remote, mountainous region. The weather at the time was characterized by drizzle, low cloud cover with a base of approximately 500 feet, and limited visibility.
After completing the technical work, the crew prepared for departure. During the takeoff sequence, the pilot performed a hover to check the surrounding area. The pilot then initiated a left yaw to clear the immediate vicinity before accelerating forward and climbing while turning to the right. During this maneuver, the main rotor blades struck two of the radio mast's stay wires. The impact severed the wires and caused the upper portion of the 70-meter tall radio mast to collapse. The pilot managed to abort the flight and performed a controlled landing approximately 80 to 90 meters from the original takeoff point. There were no injuries to the pilot or the three passengers, though the helicopter sustained extensive damage.
The investigation
The Swedish Accident Investigation Board (SHK) examined the wreckage, the radio station, and the pilot's actions. The investigation focused on the configuration of the radio mast's support system, which utilized stay wires anchored in two separate circles. The investigators noted that the pilot was highly experienced in flying this specific type of aircraft and was well-acquainted with the terrain and the inherent risks of flying near radio installations.
Technical analysis of the site revealed that the stay wires were difficult to see from the air, especially given the low cloud base and misty conditions. The investigation also looked into the organizational procedures of the helicopter operator and the existing regulations regarding flight near radio masts.
Findings
- The pilot failed to verify the exact spread of the stay wires or the location of their anchor points prior to takeoff.
- Because the top of the mast was obscured by low clouds, the pilot incorrectly assumed the mast was a shorter structure with a simpler, single-circle anchoring arrangement.
- The main rotor striking the stay wires was the direct cause of the accident.
- There were no established flight procedures for operating helicopters in the immediate vicinity of radio masts.
- There were no regulatory requirements for the marking of stay wires or their anchor points to improve visibility for pilots.
Safety action
Following the incident, the helicopter operator updated its manual to classify any takeoff or landing within 300 meters of a radio mast as a "special operation," requiring specific safety protocols. Additionally, the mast operator began a trial program to mark the outer anchor points with warning signs to increase visibility.