ERA10LA362

The pilot stated that he was conducting an aerial application flight when the low rotor rpm audio warning sounded. The pilot elected to fly the helicopter for another 30 minutes to ensure normal operation. Shortly thereafter, about 200 feet above ground level and at 70 knots, the low rotor rpm audio warning sounded again. The pilot lowered the collective to restore rotor rpm, but engine and rotor speed accelerated through the upper limits. The pilot then reduced the throttle to idle and performed an autorotation. The helicopter landed hard into a salt marsh, buckling the tail boom. The pilot did not report any flight control anomalies with the helicopter. A postaccident examination of the governor drive housing and driveshaft assemblies revealed that the inner and outer raceways were "frosted" in the ball tracks. Additionally, the ball tracks were offset from the center of the raceway in a manner consistent with a thrust load towards the driveshaft nut, relative to the drive housing. The ball track offset was not circumferentially uniform, suggesting that the bearing inner races were misaligned relative to the outer bearing races. In general, such misalignment typically results in excessive forces and subsequent fatigue failure of the ball separator. The failure of the drive bearings caused the power turbine governor to provide the incorrect signal to the main fuel control. A review of the engine records indicated that the last overhaul of the power turbine governor was at 1,942.9 hours time since new. The power turbine governor has accumulated an additional 1,590 hours time since overhaul. The power governor turbine time before overhaul (TBO) time is 2,000 hours.

On July 15, 2010, at 1358 eastern daylight time, a Garlick Helicopter, OH-58A+, N802JB, registered to and operated by Horizon Helicopters LLC, experienced a hard landing in a salt marsh following a loss of the main rotor rpm control near Rowley, Massachusetts. The aerial application flight was operated under the provisions of 14 Code of Federal Regulation Part 137 with no flight plan filed. Visual meteorological conditions prevailed. The certificated commercial pilot and passenger reported no injuries, and the helicopter was substantially damaged. The flight departed Kent's Island road, Newbury, Massachusetts, at 1342. The pilot stated that he was performing an aerial application when the low rotor rpm audio warning sounded. The collective was lowered and the rpm returned to normal. The pilot elected to fly the helicopter for another 30 minutes to ensure normal operation, and the helicopter operated normally. Shortly thereafter, while in cruise flight at approximately 200 feet above ground level at 70 knots, the low rotor rpm audio warning sounded again. The collective was lowered to restore rotor rpm, but engine and rotor speed accelerated through the upper limits. The collective was then increased to load the engine and main rotor to prevent an over-speed. This attempt had no noticeable effect and, subsequently, the pilot rolled the throttle to idle, performed an autorotation, landed hard, and buckled the tail boom. The pilot did not report any flight control anomalies prior to the accident. A Federal Aviation Administration inspector examined the helicopter. Flight control continuity was confirmed from the cockpit through the tail rotor system, and from the cockpit cyclic and collective controls through the main rotor head. Further examination of the helicopter revealed that the power turbine governor was damaged, and removed for further examination. The power turbine governor was examined by representatives of the power turbine governor, bearing and engine manufacturers, under the supervision of the FAA inspector, on September 1 2010. Examination of the drive housing and drive shaft assemblies revealed that the inner and outer races were "frosted" in the ball tracks. Further examination of the driveshaft revealed that the bearing ball separators were damaged. A review of the engine records indicated that the last overhaul of the power turbine governor was completed at 1,942.9 hours time since new. The power turbine governor had accumulated an additional 1,590 hours time since overhaul. The power governor turbine time before overhaul (TBO) time is 2,000 hours.