Accident Sequence
During a night flight, the helicopter was in level flight at about 1,400 feet MSL over a lake. The student pilot began a left turn at a forward airspeed of about 45 to 50 knots. The CFI then took over the controls to assist with the coordinated turn and noticed that the cockpit turn indicator showed the helicopter was slipping. The CFI applied left pedal to correct, and as soon as the left pedal was applied, the airframe shuddered and started to yaw to the right. The airspeed decreased and the helicopter began to spin rapidly to the right. The CFI applied full left pedal, but the helicopter continued to spin right. After lowering the collective and reducing the throttle, the spinning stopped. The CFI then lowered the nose and maneuvered the helicopter toward shallow water near the heavily vegetated shoreline, flaring and pulling up on the collective to cushion the landing. The helicopter came to rest on its left side in the shallow water.
Examination Findings
Examination of the helicopter revealed damage to the splined coupling at the aft end of the forward tail rotor drive shaft segment. Removal of the dust cover for the coupling showed that the screw and washer (part numbers AN501A10-4 and AN960-10) were loose, with several threads stripped, allowing grease to weep during operation. The forward tail rotor drive shaft assembly (part number 47-644-18-9) had been replaced on January 29, 2001. The helicopter had accumulated 70 hours of flight time since the last 100-hour inspection and 23 hours since the last 50-hour lubrication.