What happened
On May 16, 2012, at approximately 19:56, a Robinson R44 Astro helicopter, registration OH-HZH, crashed into a boggy area below the western slope of Rasivaara hill near Juuka, Finland. The aircraft was engaged in a branch sawing mission along a power line.
After approximately 20 minutes of sawing operations, the pilot, flying solo, attempted to transition to a new support base to inspect the conditions of the next section of the power line. The pilot was flying at roughly 20 knots and 200 feet above the ground, following the line. As the aircraft approached the western slope of Rasivaara, the pilot increased the pitch to slow the aircraft, which caused both airspeed and altitude to decrease.
Upon reaching the edge of the boggy area, the pilot experienced a sensation of insufficient engine power. Rather than jettisoning the heavy branch saw attached to the aircraft, the pilot attempted to lower the equipment to the ground. Once the saw made contact with the terrain, the helicopter continued to sink, leading to an uncontrolled impact and the total destruction of the aircraft. The pilot sustained minor injuries, and no fire occurred.
The investigation
The investigation focused on the technical state of the aircraft, the pilot's training, and the operational configuration of the sawing equipment. Technical examination of the OH-HZH revealed no mechanical failures or malfunctions that contributed to the accident. The pilot reported no unusual noises, vibrations, or warning system alerts prior to the impact.
However, investigators found that the sawing equipment attached to the helicopter was heavier than the equipment described in the company's Operations Manual. This increased weight placed the longitudinal center of gravity near the aft limit. Additionally, the engine was noted to be worn, which likely reduced its performance and diminished the available power reserve.
Findings
The primary cause of the accident was the pilot's excessive focus on the sawing conditions and the suspended load, which led to a loss of situational awareness and an incorrect assessment of the flight conditions. This resulted in the use of a control technique unsuitable for the situation.
Contributing factors included:
- A flight profile requiring high power, combined with the effects of a headwind and downward air currents.
- The failure to jettison the saw load as instructed by the company's Operations Manual.
- The pilot's diminished alertness due to long working hours.
- A specialized control technique used during sawing operations that necessitated limiting the use of the collective pitch lever due to low power reserves.