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The US Federal Aviation Administration (FAA) has issued an emergency airworthiness directive (AD) for all Sikorsky S-92A tail rotor pitch change shaft assemblies to help prevent loss of tail rotor control and possible loss of control of the helicopter.
The directive, 2016-24-51, was prompted after an S-92 operator recently reported losing tail rotor control while the helicopter was in a hover.
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A preliminary investigation of the incident found binding had occurred in the tail rotor pitch change shaft assembly double row angular contact bearing which resulted in reduced tail rotor control.
Investigators also found signs of excessive heat in the assembly – an indicator of a binding bearing.
Effected assembly part numbers include 92358-06303-041 or 92358-06303-042 with less than 80 hours time in service for all S-92As certificated in any category.
After reviewing Sikorsky’s Alert Service Bulletin, the FAA said its emergency AD required all tail rotor pitch change shaft assemblies with less than five hours in service since new or since overhaul must be removed from service before further flight.
All assemblies with more than five hours in service are to receive a once off borescope and visual inspection to determine the condition of the bearings and the Teflon seal and snap ring.
In August 2007, the FAA had also issued an AD for inspecting S-92A tail rotor pitch change shaft and bearing assembles.
According to the Civil Aviation Safety Authority’s aircraft register, there are currently 11 S-92As registered in Australia.
