On May 5, 2004, at 1920 Pacific daylight time, a Robinson R-22 Mariner, registered to a private individual DBA Emerald City Leasing, operated by Hillsboro Aviation as a 14 CFR Part 91 instructional flight experienced a loss of engine power followed by an autorotation. The helicopter landed hard subsequently rolling over in a field located about 1/4 mile west of the Chehalis-Centralia Airport, Chehalis, Washington. Visual meteorological conditions prevailed at the time and a visual flight rules flight plan was filed, but not activated. The helicopter was substantially damaged, however, the flight instructor and private pilot were not injured. The flight originated from Seattle, Washington, about 1845.

The flight instructor stated that the flight originated earlier in the day from Hillsboro, Oregon, to transport the helicopter to Seattle for maintenance. At the completion of the maintenance work, the helicopter was being flown back to Hillsboro, with a stop in Chehalis for fuel.

The flight instructor reported that they were maneuvering east to west, about 1,000 feet above ground (AGL) level, to cross the airport at mid-field to check the wind conditions with the intent to make a left downwind for runway 33. During this maneuver, the engine suddenly and without warning quit. The flight instructor took control as the private pilot attempted to restart the engine, however, there was only a "clicking" sound heard and the engine would not start. The flight instructor noted that the warning lights came on and all the gauge indications dropped.

The flight instructor initiated an autorotation to an open cow pasture. The flight instructor stated that he initiated the flare about 30 feet above ground level and raised the collective to cushion the landing, however, he did not apply enough "right pedal which caused the helicopter to yaw to the left and make contact with the right skid." The right skid collapsed and the helicopter rolled over, coming to rest on its right side.

About three minutes after evacuating the helicopter, the private pilot reported that he heard a "pop" that sounded like a vapor release then noted some fuel spill coming out near the main rotor transmission.

Throughout the approximate hour long flight and just prior to the loss of engine power, both pilots reported normal engine indications except for the flight instructor felt that he "...heard some weird droning noises coming from the engine." The instructor reported that he checked the gauges and found nothing out of the ordinary.

A witness to the event reported that he heard the helicopter, but thought little of it until " sounded odd - like it got a higher pitched whine to it." The witness observed the helicopter moving quickly and "dropping faster than normal." The helicopter descended to about 10 feet above the hay field and "skimmed over the hay for probably 50' - 100' - then the helicopter made a "nose up/tail down" drastic attitude change and stalled out into the field..."

The following day, the helicopter was righted for recovery. The battery was reconnected and the engine was started. The engine started immediately using the existing fuel on board and was run for about three minutes at idle power before it was shut down.

The airframe and engine were subsequently transported to Robinson Helicopter Company, Torrance, California. On May 27, 2004, in the presence of NTSB Air Safety Investigators from the Southwest Regional Office, the engine and systems were inspected. During the inspection no evidence of a mechanical failure or malfunction was found. The fuel lines, venting system and fuel tank were all inspected and found no obstructions or contaminants. (see attached engine inspection report)

Prior to engine overhaul, the engine was placed in and run on a dynamometer for more than one hour. No discrepancies were noted during the test run. The engine was found to meet normal test specifications.

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