Accident Overview
On July 15, 2010, at 1358 eastern daylight time, a Garlick Helicopter OH-58A+, registered as N802JB and operated by Horizon Helicopters LLC, experienced a hard landing in a salt marsh following a loss of main rotor rpm control near Rowley, Massachusetts. The aerial application flight was conducted under 14 Code of Federal Regulation Part 137 without a filed flight plan. Visual meteorological conditions prevailed at the time. The certificated commercial pilot and passenger reported no injuries, and the helicopter sustained substantial damage. The flight had departed from Kent's Island Road, Newbury, Massachusetts, at 1342.
Pilot Account
The pilot reported that while performing an aerial application, the low rotor rpm audio warning activated. He lowered the collective, and rotor rpm returned to normal. He elected to continue flying for approximately 30 minutes to ensure normal operation, during which the helicopter performed without issue. Shortly thereafter, while in cruise flight at about 200 feet above ground level and 70 knots, the low rotor rpm warning sounded again. The collective was lowered to restore rotor rpm, but engine and rotor speed accelerated through the upper limits. The pilot then increased the collective to load the engine and main rotor and prevent an overspeed, but this had no noticeable effect. Subsequently, the pilot rolled the throttle to idle, performed an autorotation, landed hard, and buckled the tail boom. The pilot reported no flight control anomalies prior to the accident.
Examination Findings
A Federal Aviation Administration (FAA) 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. Examination of the helicopter revealed that the power turbine governor was damaged, and it was removed for further analysis.
On September 1, 2010, the power turbine governor was examined by representatives of the power turbine governor manufacturer, bearing manufacturer, and engine manufacturer, under FAA supervision. Examination of the drive housing and drive shaft assemblies showed 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.
Maintenance History
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 manufacturer-specified time before overhaul (TBO) for the power turbine governor is 2,000 hours.