Aircraft and Flight Details
The aircraft involved was a Robinson R44 helicopter, registration G-NIOL, manufactured in 2003 and powered by one Lycoming O540 piston engine. The pilot, aged 41, held a JAR Private Pilot's Licence and had accumulated 116 flying hours, 59 of which were on type. The flight was a private trip from Lydd to a landing site near Heathfield, West Sussex. Pre-flight checks were normal, except for the addition of one litre of oil. Surface temperature at start was +6°C.
Flight Sequence
While cruising at an altitude of 1,200 feet and an indicated airspeed of 100 knots, the pilot passed the southern edge of a rain shower. He applied carburettor heat to raise the induction air temperature from just below +10°C to approximately +12°C to +14°C due to the possibility of increased moisture. Shortly after, the pitot-static instruments began fluctuating, with variations in indicated airspeed of 20-30 knots, vertical speed excursions up to 1,000 feet per minute, and similar effects on the altimeter, although no major turbulence was present. The pilot reduced speed to 70 knots to assess the effect.
As the helicopter decelerated, the pilot noticed the governor opening the throttle in response to a slight yaw. Engine and rotor RPM then began to decay; the pilot found the throttle already fully open. He corrected the yaw with right pedal, lowered the collective, and rolled the throttle closed to enter autorotation. Once autorotation was established, he raised the collective slightly to reduce rotor speed and observed that the engine was still running. Attempting a powered recovery, he opened the throttle; the engine RPM rose but appeared unable to deliver power to the rotors. The pilot's recollection became hazy, but he believed he raised the collective to try to power the rotor system. His focus on power recovery allowed the rotor RPM to fall "dangerously low." The helicopter then entered what the pilot described as a "freefall" with uncontrollable yawing and a high rate of descent. He managed to obtain forward airspeed, which reduced the rate of descent. Believing the helicopter could not be recovered, he selected a large garden with trees at the rear for a run-on landing. The touchdown occurred with considerable forward speed, and the helicopter ran into trees, coming to rest severely damaged. The pilot sustained minor injuries, evacuated without assistance, and emergency services attended; there was no fire.
Post-Accident Examination
The engine was removed, inspected, and fitted with three replacement dented rocker covers. A full pass-off test on a test bed showed no anomalies, and the engine exceeded its rated power. Fuel was found in the carburettor shortly after the accident. The carburettor air temperature gauge was calibrated and found to under-read by 5°C at a true temperature of +10°C; it was not determined whether this resulted from impact forces. No defects were found in the engine or its accessories that could explain a loss of power.