NTSB Identification: ERA10LA362
14 CFR Part 137: Agricultural
Accident occurred Thursday, July 15, 2010 in Rowley, MA
Probable Cause Approval Date: 10/17/2011
Aircraft: GARLICK HELICOPTERS INC OH-58A+, registration: N802JB
Injuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

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.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The failure of the power turbine governor internal driveshaft bearings, resulting in the failure of the governor.

Full narrative available

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