R22 Upper and Lower Clutch Actuator Bearings

The failure of either of the actuator bearings in-flight could cause loss of power to the rotor system and could result in a serious accident as the main drive V belts will slip or be destroyed.

The following information was particularly important to the ball bearing races fitted before the Robinson Factory upgraded to roller bearings. However, the same principles still apply as the roller bearing lubrication can very occasionally fail especially in harsh operating conditions.

The upper actuator bearing is located on the clutch shaft and the lower actuator bearing is located on the fan shaft.  The first indication of an impending bearing failure is usually a noticeable increase in bearing noise.  The noise will almost always start at least several hours before the bearing actually fails and long before there is any increase in the bearing temperature – though some pilots disagree with this.

To detect a possible failure of the upper or lower clutch actuator bearings, listen to the sound of the drive system both during start-up and during shut-down.  The failing bearing will produce a loud whine, rumble, growl, or siren sound.  Upon hearing an unusual noise, ground the aircraft and thoroughly inspect the bearings.

Just before complete failure of an actuator bearing, the clutch light bulb filament may flicker constantly (on and off in less than one second).  This should not be confused with its normal on-off re-tensioning in-flight (on for 1-6 seconds then off).  Some pilots have noticed the clutch light bulb filament start to glow very slightly on and off – rather than as a bright normal light – up to an hour before a pronounced flicker became evident.

Flight should not be resumed until the cause of the flickering clutch light has been determined and a resultant safety decision made.

TC

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