What happened
On May 7, 2009, a Bell 412EP helicopter, registration OH-HVK, operated by the Finnish Border Guard, crashed during a multi-agency training exercise near Ali-Vekkoski, Porvoo. The mission involved searching for and apprehending fugitives in the terrain. Upon spotting a target, the pilot-in-command decided to land a six-person tactical team in a clearing ahead of the subject.
The crew was unfamiliar with the chosen landing site, which was located behind a wooded area relative to the approach. To reach the site, the pilot accelerated the aircraft to 107 knots at an altitude of approximately 250 feet. As the aircraft approached the landing zone, the pilot attempted to decelerate by lowering the collective and applying aft cyclic. This maneuver caused the main rotor RPM to surge above 104.5%, triggering a high-RPM warning. As the airspeed bled off and the pilot subsequently raised the collective, the resulting rotor drag caused the RPM to drop below 95%, triggering a low-RPM warning.
During this period, the helicopter entered a developing vortex ring state. The pilot attempted to recover by raising the collective, but the sink rate continued to increase, reaching a maximum of approximately 1,100 ft/min. The aircraft struck the ground approximately four seconds after the low-RPM warning. The impact was severe enough to fracture the landing gear and damage the fuselage sub-floor. There were two minor injuries among the passengers.
The investigation
The investigation confirmed that the helicopter was airworthy, with the weight and center of gravity within permissible limits. No technical malfunctions or mechanical failures were identified. The weather conditions were suitable for the mission, and the crew's licenses and experience were sufficient. The investigation focused on the aerodynamic state of the rotor and the pilot's inputs during the deceleration phase.
Findings
The immediate cause of the accident was the helicopter entering a vortex ring state during landing, under conditions where corrective actions were no longer possible.
Contributing factors included:
- High approach speed and a late deceleration maneuver involving significant power changes in a heavily loaded aircraft.
- Deficiencies in cockpit resource management, specifically regarding the monitoring of checklists, speed, altitude, sink rate, and wind direction.
- Inadequate observation of the aircraft's flight state and the unfamiliar landing area due to the crew's intense focus on the tactical mission.
- Deficiencies in standardized procedures and instructional guidelines for this specific mission type.