Introduction
This article summarizes the factual information from the Danish Accident Investigation Board (AIB) safety investigation bulletin 2023-502 concerning an accident involving a Robinson R44 Clipper II helicopter, registration OY-HFS, on 4 October 2023.
History of Flight
The flight was a private VFR flight from a private helipad near Varde to Kolding/Vamdrup (EKVD). Approximately 10 minutes after departure, near Holsted, the engine and rotor RPM dropped to just below 70%. The pilot declared an emergency (Mayday) to Esbjerg Information but successfully recovered the RPM; the governor controller/Engine Monitoring Unit (EMU) reactivated above 80% engine RPM, and normal engine governing resumed. The pilot cancelled the emergency and continued toward EKVD.
During a left-hand approach to runway 25 at EKVD, after turning to the final leg, engine and rotor RPM increased to 120%. The pilot did not attempt to recover from the high RPM condition. Instead, he initiated an autorotation and declared an emergency to Vamdrup Information. The helicopter made a hard landing in a field with low vegetation, sustaining substantial damage. The pilot reported being uninjured, and the Aerodrome Flight Information Service activated the emergency response plan.
Injuries and Damage
No injuries occurred to the pilot or any other persons. The helicopter sustained substantial damage to the landing gear skid (bent), firewall/bulkhead, main rotor blades, and tail boom. No other damage was reported.
Personnel Information
The 53-year-old male pilot held a valid Private Pilot License (Helicopter) issued by the Danish Civil Aviation and Railway Authority (DCARA) on 24 May 2022. The latest Proficiency Check was completed on 20 April 2023, with a valid R44 rating until 31 May 2024. His Class 2 medical certificate was valid until 27 January 2024. Total flying experience was 132 hours and 35 minutes, all on type. Nothing from training records indicated prior issues with governor failures or RPM control problems.
Aircraft Information
The aircraft was a Robinson R44 Clipper II (OY-HFS) powered by one Lycoming IO-540-AE1A5 engine. The AIB noted that preventive measures for engine RPM runaways, including emergency procedures and a safety alert, were available at the time of the accident.
Meteorological Information
The accident occurred in daylight under Visual Meteorological Conditions (VMC). Specific weather data from the terminal aerodrome forecast and routine weather reports were documented in the investigation but no further characterization is provided here.
Communication
During the low RPM event, the pilot contacted Esbjerg Information on the emergency frequency. During the high RPM event, he contacted Vamdrup Information (EKVD AFIS) and declared a Mayday. After landing, the pilot informed Vamdrup Information that he was uninjured.
Analysis and Conclusions
The AIB conducted a technical investigation including data from the governor controller/EMU and ADS-B data. The analysis covered the pilot's handling during both RPM underspeed and overspeed events, as well as adherence to procedures. The safety investigation did not identify the cause of neither the low engine RPM state nor the high engine RPM state.
Probable Cause
The probable cause of the accident was not determined by the investigation.