What happened
On August 22, 2015, a Robinson R-44 Raven II helicopter, registration SP-TVN, was conducting a filming mission for the Air Show 2015 at Radom-Sadków Airport. While maintaining a hover at approximately 150 meters for television coverage, the pilot noticed the engine tachometer exceeding 110% RPM.
Upon deciding to abort the mission and return to Radom-Piastów, the engine began operating loudly with increasing RPM. As the pilot attempted to reduce power using the collective and throttle, the rotor RPM simultaneously dropped, causing a loss of altitude. Faced with approaching trees and unable to clear them, the pilot attempted an emergency landing in an open field using a technique similar to autorotation. However, the aircraft struck the ground with high vertical velocity and overturned on its left side. The pilot and camera operator sustained two light injuries, and the aircraft was destroyed.
The investigation
The PKBWL examined the wreckage and the pilot's flight history. Investigators noted that the engine was functional at the time of the crash and the aircraft's maintenance documentation was in order. The investigation also reviewed a previous incident from May 2015 involving the same aircraft and pilot, where similar engine RPM fluctuations had occurred but remained unresolved.
Findings
- The primary cause of the accident was the pilot's loss of control over the helicopter due to improper engine RPM management.
- The investigation suggests that a sudden external factor, such as a wind gust, likely initiated the RPM fluctuations. The pilot's manual corrections overlapped with the delayed mechanical response of the engine governor, creating a resonant effect that amplified the instability.
- A contributing factor was the failure to investigate and resolve a similar engine instability incident that had occurred on the same aircraft earlier that year.