What happened
On March 25, 2012, a Robinson R44 helicopter, registration PH-WQW, was preparing for a return flight from a helipad near Zwolle to Lelystad Airport. The flight was part of a passenger trip involving two passengers. During the startup phase, the pilot engaged the engine and increased rotor RPM to approximately 60%.
As the pilot worked through the checklist, the aircraft began to vibrate and slide across the wooden platform. The pilot attempted to stabilize the aircraft by searching for the neutral point on the cyclic, but the vibrations intensified, causing the helicopter to bounce between its skids and rotate approximately 270 degrees. In an attempt to prevent the aircraft from sliding off the edge of the platform, the pilot pulled up on the collective. However, due to the low rotor RPM, the aircraft could not maintain altitude and instead entered an uncontrolled flight phase, eventually striking the surface of a nearby pond. The helicopter floated briefly before sinking to the bottom. All three occupants successfully exited the aircraft and swam to safety, sustaining no injuries.
The investigation
The Dutch Safety Board (OVV) examined the aircraft and the condition of the helipad. Technical inspections of the PH-WQW revealed no mechanical failures. While the collective friction was found to be removed, the exact setting of the cyclic friction could not be determined.
The investigation also scrutinized the helipad, a wooden structure on a metal frame. Although an inspection by the ILT later revealed that the platform was in poor condition—with loose, warped, and broken planks—the OVV concluded that the platform's state was not the cause of the accident, as there was no evidence the skids had caught on any uneven surfaces.
Findings
The investigation identified a complex chain of aerodynamic factors. During the startup phase, the main rotor was observed in an unusual position, suggesting the pilot may have held the cyclic away from the neutral point, which generated the initial vibrations. As the pilot attempted to correct this, the collective may have been inadvertently raised, reducing the friction between the skids and the smooth wooden platform.
At a low rotor RPM of 60-70%, the tail rotor's effectiveness was significantly reduced. This allowed a wind vane effect to initiate a rotation around the vertical axis. As the aircraft rotated into a different wind angle, the airflow became unstable, further increasing the pilot's workload. The pilot's subsequent attempt to lift the aircraft with the collective, while the aircraft was still under low power and experiencing high workload, ultimately led to the uncontrolled descent into the water.