What happened
On August 26, 2017, a Robinson R44 RAVEN I, registration OK-SCI, was performing a series of short recreational flights for guests at a family celebration near the village of Vnorovy. During the 14th flight, shortly after takeoff, the pilot attempted to transition from a climb to level flight. During this maneuver, the pilot noticed that both the engine and main rotor RPM indicators had reached the upper red line.
In response to the overspeed condition, the pilot decided to perform an immediate emergency landing in a nearby field. The helicopter touched down with a slight forward slide. As the skids contacted the ground, the aircraft experienced a sudden pitch and movement. The pilot instinctively applied aft cyclic input, which tilted the rotor disc and caused the main rotor blades to strike the tail boom. The impact severed the upper half of the tail boom tube and damaged both rotor blades. Following the landing, the pilot performed a brief check and returned to the original takeoff site, where the damage was discovered by local citizens.
The investigation
The ÚZPLN investigation examined the pilot's actions, the aircraft's mechanical condition, and the takeoff/landing site. The investigation established that the pilot, while experienced on the type, had inadvertently bypassed the governor's effectiveness by firmly gripping the throttle lever, preventing the governor from regulating RPM during the transition to level flight.
Technically, the aircraft was found to be in good condition, with no mechanical failures or engine malfunctions identified. The investigation also noted that the chosen landing area was within a residential area and less than 100 meters from buildings, which did not comply with local aviation regulations regarding takeoff and landing sites.
Findings
- The primary cause of the accident was the contact between the main rotor blades and the tail boom, resulting from improper control inputs during flight and an inappropriate cyclic reaction during the forced landing.
- The pilot's firm grip on the throttle lever effectively neutralized the governor's ability to regulate engine and rotor RPM during the change in flight regime.
- The pilot failed to transition the helicopter into a hover before touchdown, leading to a landing with a forward slide.
- The pilot did not perform a thorough visual inspection of the aircraft immediately following the emergency landing.
- The selected takeoff and landing area was located within a residential zone and was in violation of distance requirements from buildings.