On June 14, 2024, at 1827 eastern daylight time, an experimental amateur-built Rotorway Exec 162F helicopter, N99TE, was substantially damaged when it was involved in an accident near Alva, Florida. The airline transport pilot and pilot-rated passenger were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that they performed a preflight inspection and as a part of the preflight, he checked the tail rotor drive belt tension with a spring scale and it was within limits at 10 lbs. Shortly after departing from his residence, while flying at an altitude between 200 and 300 ft msl, he handed off the controls to the passenger. Upon reaching a small grass airstrip the passenger flew a high “recon” flight in an easterly direction. During the approach, at an altitude of about 150 ft agl with an airspeed of 20-30 mph, the passenger made a cyclic correction to stay over the runway centerline. He reported that after the correction he noticed the rotor rpm was below 100% so he increased the throttle. He reported that as the helicopter passed through effective translational lift (ETL) it began to yaw to the left with full right pedal applied. The pilot took control of the helicopter and applied forward cyclic in combination with right anti-torque pedal input to correct the yaw. However, the helicopter descended in a sweeping left turn with full right anti-torque pedal applied and he was unable to regain directional control before the helicopter contacted the edge of an irrigation ditch during the landing attempt. The helicopter rolled over and came to rest on its right side, which resulted in substantial damage to the rotor blades and a large crease in the tail boom. The pilot reported that the engine operated as expected for the duration of the flight and no abnormal vibrations or sounds were noted. Additionally, all flight controls were operating as expected until the unanticipated yaw began. An FAA inspector examined the helicopter after the accident and found that the tail rotor bolt tensioner assembly was not secured. The right side of the tail rotor drive belt jam nut and the self-locking nylon nut were loose (see figure 1). The nuts, when properly secured, placed tension on the tail rotor drive belt. There was no access to physically view these critical nuts during a preflight inspection.

Figure 1. Examination of tail rotor assembly; tail rotor drive belt nuts out of position.