The pilot of the Bell Jet Ranger reported that while cruising at about 2,500 ft AGL, the rotor RPM indication decreased to zero. He initiated auto-rotation immediately by lowering the collective pitch. The controls were very stiff, however all engine parameters were normal. The helicopter descended at higher than normal speed and landed heavily. The right skid crosstube support failed and the aircraft rolled onto its side. Both occupants vacated the wreckage with minor injuries.
The pilot reported that he did not hear the low rotor alarm and did not notice the low rotor RPM caution light illuminate.
Investigation determined that the drive spline and coupling to the hydraulic pump and rotor tachometer generator were devoid of lubrication and worn to the degree that drive to both units had failed. This resulted in the loss of hydraulic power to the controls and the loss of the main rotor speed indication.
The low rotor RPM sensor which provides a signal to activate the low rotor alarm and the low rotor RPM caution light was tested and functioned normally. However, it is likely that the pilot did not notice the low rotor RPM warnings, due to his immediate initiation of an auto-rotation, and the ambient light conditions. The warning horn is cancelled by a cut-out switch on the collective pitch handle when the handle is lowered as in the case of an auto-rotation. As the helicopter was tracking south at the time, the bright sun from the northeast would have made illumination of the low rotor RPM caution light difficult to distinguish.
Investigation of the maintenance requirements for the helicopter found that, prior to January 1998, the hydraulic pump drive splines were required to be lubricated by hand every 1200 hours or twelve months, whichever came first, or under extreme operating conditions, every 300 hours. In January 1998 the manufacturer issued a revised manual with a changed requirement for the Bell 206B III model to lubricate the hydraulic pump drive splines every 300 hours with no calendar requirement.
The accident helicopter had only accumulated about 90 hours time in service since January 1998 and 217 hours since the initial issue of its Australian certificate of airworthiness in 1990.
