On August 5, 2000, at 1909 eastern daylight time, a homebuilt Rotorway 152 helicopter, N11662, was substantially damaged when it rolled over after a forced landing to a soybean field in Ravenna, Ohio. The certificated airline transport pilot and passenger were not injured. Visual meteorological conditions prevailed for the local personal flight that originated at the pilot's farm, approximately 1830. No flight plan was filed for the flight conducted under 14 CFR Part 91. In a written statement, the pilot said the helicopter was in cruise flight at 70 knots approximately 600 feet above ground level (agl) when he heard a loud report from behind the cockpit. According to the pilot: "Took off from my farm approximately 18:30 for a pleasure flight. After about 20 [minutes] of flight we were heading east towards [passenger's] house. I heard a loud 'pop/bang' and felt a hard jerk to the left. [I] immediately reduced power and entered autorotation. Landed in a soybean field. Touchdown was normal/soft with approximately walking speed. At almost a stop, skids caught in soybeans. [Helicopter] went up on nose - straight ahead - main rotor struck ground and [helicopter] rolled over on its port side." According to the passenger: "We were flying at approximately 600 ft...when something broke and we were immediately out of control. The helicopter dropped then the nose dropped and we went into a dive. Then the pilot was able to level it before we hit the ground. Then we went over forward and we rolled." In a written statement, a witness said: "We saw the copter flying overhead...We heard a loud 'pop' and saw him descending down pretty fast. He leveled it out and I thought he landed OK, and all of a sudden it must [have] got caught in the soybean field and the nose went forward and the rotor hit the ground." During a telephone interview, the pilot said that when he heard the bang and felt the helicopter yaw, he thought the tail rotor had departed the helicopter. The pilot said that after he rolled the throttle to idle and entered autorotation, he realized that he still had tail rotor authority. He said that during the descent, the engine was running smoothly at idle, and that he chose to continue the autorotation at idle power. The pilot said he based his decision on his concern that a resumption of operating power would initiate another adverse yaw event. According to the pilot: "I thought I lost my tail rotor, but then I realized I had tail rotor authority. I thought about rolling the throttle back on, but I was afraid that it would pop like that again, so I just left the power off. I mean, I had [the autorotation] locked. My blood pressure didn't even go up. I wasn't worried at all. "Hell, the only problem was that 3-foot high soy beans and helicopter skids are not compatible." The pilot held an airline transport pilot certificate with ratings for airplane multi-engine land. He also held a commercial pilot's certificate with ratings for airplane single engine land, single engine sea, and rotorcraft helicopter. The pilot was issued a first class medical certificate on May 2, 2000. He reported 18,935 hours of total flight experience. He reported 106.7 hours of flight experience in the Rotorway, 7 hours of which were in the last 90 days. The pilot said he completed the 100 hour and annual inspections on the helicopter during the months of June and July 2000. He said he replaced bearings and bushings in the rotorhead and replaced spark plugs and adjusted points in the engine at that time. Inspectors from the Federal Aviation Administration (FAA) examined the helicopter, on August 8, 2000. In a telephone interview, one of the inspectors said examination of the wreckage revealed no pre-impact anomalies. He said, "We looked at belts, drives, clutches and the engine. We couldn't find anything wrong. The engine started up and it ran all right." The pilot said his post-accident inspection of the helicopter revealed a loose spark plug wire on the #2 spark plug. He said that he was sure the loose wire caused the interruption in power during the flight. According to the pilot: "I did an annual on the helicopter about 6 hours before the accident, and my friend helped me with the inspection. He worked on one side of the engine, and I worked on the other. I never double-checked his work. Well, the number 2 spark plug wire was loose. You really have to snap it down. I should have checked his work and I didn't." The pilot reported that other than the loose spark plug wire, there were no mechanical deficiencies with the helicopter. Weather reported at Akron, Ohio, 14 miles southwest of 29G was clear skies with winds from 210 degrees at 5 knots.