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Summary

Summary

Soon after takeoff the right engine suffered an underspeed condition and was shut down. The aircraft was returned to Wynyard for a single engine landing. Maintenance investigation disclosed that the overspeed governor had failed. The governor was removed and sent to the manufacturer for assessment and repair. The manufacturer tested the governor, finding it to be noisy in operation. The high speed setting was found to be low, the governor was uncontrollable at the balance point and was unable to give an overspeed flow. When the unit was stripped small pieces of aluminium were found in the solenoid body, along with other non metallic particles. The manufacturer did not detail the origin of the contaminants. A series of failures to governors, pitch control units and feathering solenoid valves fitted to this aircraft type has been traced to electrokinetic corrosion and a particular brand of propeller gearbox oil. The operator has changed to a different oil and incorporated a manufacturer's modification designed to gain equal electrostatic potential by improving the bonding between the propeller and gearbox. The operator advised that these measures appear to have reduced the rate of deterioration of the components.
 
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