What happened
On September 1, 1997, a Hughes 369D helicopter, registration OH-HCA, was performing utility work near Kotka, Finland. Operated by Copter Action Oy, the flight was part of a mission to transport and install utility poles for an electrification project on Pitkäsaari. Having successfully delivered 15 poles earlier in the day, the pilot attempted to move a third pole to a temporary storage area on the island.
The incident occurred at approximately 16:15 local time. While maneuvering the 180 kg pole, the pilot approached at a lower altitude and a different angle than previous trips. The load struck trees, causing the pole to swing violently. As the pilot attempted to land the load, the base of the pole did not slide across the ground but instead pivoted into a vertical position. Because the pilot could no longer see the load in the aircraft's mirrors, the main rotor struck the lifting sling at a distance of only about 10 cm from the rotor plane.
The impact caused significant damage to the main rotor blades and the tail boom. The force of the strike was so violent that it tore the cargo hook from the aircraft's underside, rupturing the fuselage and the fuel tank. This resulted in a continuous fuel leak during the return flight to Sapokka. The pilot, experiencing extreme vibration that made instruments unreadable, completed the flight at a low altitude of approximately 10 meters.
The investigation
The investigation focused on the sequence of the load's movement and the pilot's decision-making during the approach. Investigators examined the aircraft's maintenance records, the pilot's experience, and the physical damage to the Hughes 369D. The investigation also looked into the operational environment, noting that the flight was conducted in uncontrolled airspace and that the operator held a specific permit to operate a single-engine helicopter in this island region.
Findings
- The primary cause of the accident was that the pilot did not abort the approach after the pole began to swing and disappeared from the rearview mirrors, resulting in the rotor striking the sling.
- The pilot's high workload and the pressure of a busy flight schedule acted as a contributing factor.
- The aircraft's structural damage, including the broken rotor blade components and the dented tail boom, worsened during the return flight due to intense vibrations.
- The impact caused a breach in the fuel tank, leading to a fuel leak throughout the duration of the return leg.
- The pilot failed to report the damage to air traffic control or the police in accordance with standard regulations, although the operator was notified that evening.