SEA96LA188

The pilot stated that he was practicing hovering and turns at an altitude of 10 feet, and was moving forward at about 5 mph, when power to the main rotor was lost due to slippage of the drive belts. He stated that he heard a sound like a rock hitting the fuselage, then the engine rpm increased from its rated rpm of 4,250 to 4,700. During recovery, the pilot pulled collective and used right cyclic to level out and maintain altitude. The helicopter slowed its descent and almost leveled out, but landed on the skids with a slight left drift. The helicopter rolled over after ground contact. The pilot held limited solo privileges for helicopters. He had first soloed a helicopter about three months before the accident and had a total of 17.2 hours of rotorcraft time. He stated that before the accident, he had just flown the helicopter for about one hour, then landed and checked the aircraft for 'tensions etc [sic]' before taking off again. According to operation and maintenance instructions furnished by RotorWay International, the main rotor drive belt tension should be checked and adjusted at new belt installation and at 30 minutes, 1 hour, 2 hours, and 10 hours of service (to prevent slippage). The aircraft and engine logbook copies submitted by the pilot contained no documentation of any checks or adjustments to the drive belt tensions after new belt installation on 7/10/96.

On August 12, 1996, approximately 0835 Pacific daylight time, a Jonas Rotorway Exec 90 kit-built experimental helicopter, N6183P, crashed at the Hermiston, Oregon airport following a loss of control during a low-altitude/low speed turn. The aircraft received substantial damage and the private pilot, who was rated for single-engine airplanes and held a limited student solo endorsement for helicopters, received minor injuries. The pilot owned and had built the helicopter and was its sole occupant at the time of the accident. Visual meteorological conditions existed and no flight plan had been filed for the local 14 CFR 91 flight from Hermiston.

The helicopter had 13.3 hours total time at the time of the accident, and was in its initial "fly-off" period per FAA experimental aircraft airworthiness certification requirements. Copies of the aircraft and engine logbooks submitted by the pilot indicated that new drive belts had been installed, and the tensions adjusted, on July 10, 1996 (eight days after the helicopter had been issued its original experimental-category airworthiness certificate) at 2.4 hours time in service. The pilot stated that at the time of the accident, he was practicing hovering and turns at an altitude of approximately 10 feet. He stated that he had just flown the aircraft for about one hour, then landed and checked the aircraft for "tensions etc [sic]" before taking off again. He reported:

At about 10' altitude while turning left at about 5 MPH I heard a sound like a rock hitting the fuselage and then the engine RPM increased from 4250 [the engine's rated RPM] to [about] 4700....I was losing altitude. My reaction was to pull collective and give right cyclic to level out and maintain altitude. The helicopter slowed descent and almost leveled out but landed on the skids with a slight left drift. Then the helicopter lifted the right skid and continued a slow roll over to the left....[It] appears that the drive belts stretched and slipped.

The FAA inspector assigned to the accident conducted an on-scene investigation the day after the accident. Her report stated: "The Pilot [sic] added excessive power during a turn, while 8-10 feet above ground. Helicopter rolled over on left side." The FAA inspector's report stated that the pilot had first soloed a helicopter on May 17, 1996 and that the pilot's helicopter solo endorsement (which was valid for hover, turns, and quick stops) was valid until mid-August 1996 (the pilot also reported that he had 17.2 hours of rotorcraft time.)

In a telephone conversation with the NTSB IIC, the president of RotorWay International (the helicopter kit manufacturer) stated that the helicopter's drive belt tension is manually adjusted. According to aircraft operation and maintenance instructions furnished by RotorWay International, main rotor drive belt tension should be checked and adjusted at new belt installation and at 30 minutes, 1 hour, 2 hours, and 10 hours of service. The aircraft operating and maintenance instructions state that if a belt becomes loose enough to slip, it will get hot and destroy the cord inside the belt. The instructions state that if the cord inside is damaged and the belt is cold, the belt will work satisfactorily until it gets warm, at which point it will stretch and slip enough to result in loss of power to the drive train. The aircraft and engine logbook copies submitted by the pilot contained no documentation of any checks or adjustments to the drive belt tensions after the July 10, 1996 new belt installation.