The pilot stated that the helicopter was given a full daily inspection. The engine had full oil and there was approximately 55 litres of fuel on board. After start, the engine was kept at idle until oil temperature was about 75 degrees. the rotors were then engaged and warm up was continued at 2000 RPM and then 2500 RPM. The magneto check showed no rough running. After pre-take-off checks, the helicopter was brought to the hover and moved forward about 6 feet, then put back on the ground for about 3 minutes while a load was placed on board. The pilot stated that after checking that all nozzles were working and pre-take-off checks were complete, he brought the helicopter to the hover. At 3200 RPM the manifold pressure was 26 inches. Transition to forward flight was normal, and height and speed began to increase. At about 60 to 70 feet agl and about 40 knots the engine note changed, and the pilot noticed RPM had reduced to about 2700. The pilot lowered the collective and wound on full throttle. A landing straight ahead was carried out with some forward speed, and during the landing the main rotor struck the tail boom and severed it. The helicopter was fitted with an NARCO 10 Emergency Locator Transmitter, which did not activate during the heavy landing.
Subsequent examination of the engine failed to reveal any defect, but engineering opinion was that the engine malfunction was most likely due to a sticking valve.