FAA, November 18, 2016 - The FAA (Federal Aviation Administration) Emergency Airworthiness Directive AD# 2016-24-51 ( click here for PDF ) was prompted by a report of an operator losing tail rotor (TR) control while in a hover. A preliminary investigation determined that binding in the TR pitch change shaft (TRPCS) assembly double row angular contact bearing resulted in reduced TR control.
The investigation also found signs of excessive heat, which is an indicator of a binding bearing. Because binding will result in bearing failure rapidly, we are limiting this Emergency AD to TRPCS assemblies with less than 80 hours time-in-service (TIS).
This Emergency AD requires, before further flight, removing from service any TRPCS assembly with less than 5 hours TIS since new or overhaul.
For TRPCS assemblies that have 5 or more hours TIS since new or overhaul, this Emergency AD requires a one-time borescope and visual inspections of the TRPCS assembly and bearing to determine the condition of the bearings. The actions in this Emergency AD are intended to detect a binding bearing, prevent loss of TR control, and possible loss of control of the helicopter.
This Emergency AD requires, before further flight, removing TRPCS assemblies with less than 5 hours TIS. This Emergency AD also requires, for TRPCS assemblies with 5 or more hours TIS since new or overhaul, borescope inspecting the TRPCS and bearing assemblies for damaged bearings and seals, purged grease with any metallic particles from the bearings, radial play in the bearings, and correct installation of the white Teflon seals, snap rings, and cotter pin, and determining whether there is free rotation in the angular contact bearing. These inspections are required before further flight for TRPCS assemblies that have between 5 and 15 hours TIS since new or overhaul. For TRPCS assemblies with more than 15 hours TIS, these inspections are required within 20 hours TIS or before reaching 80 hours TIS, whichever occurs first. If there is any damage to the bearings, restrictive radial play, purged grease with metallic particles, or missing or incorrect installation of the white Teflon seals, snap rings, or cotter pin, this Emergency AD requires replacing the TRPCS and bearing assembly before further flight.
Differences Between This Emergency AD and the Service Information:
The ASB requires operators to contact Sikorsky if there are any discrepancies, this Emergency AD does not. The ASB allows 20 hours TIS to perform the visual bearing inspection if the borescope inspection has already been performed, while this Emergency AD allows 20 hours TIS for TRPCS assemblies with 15 or more hours TIS.
The investigation also found signs of excessive heat, which is an indicator of a binding bearing. Because binding will result in bearing failure rapidly, we are limiting this Emergency AD to TRPCS assemblies with less than 80 hours time-in-service (TIS).
This Emergency AD requires, before further flight, removing from service any TRPCS assembly with less than 5 hours TIS since new or overhaul.
For TRPCS assemblies that have 5 or more hours TIS since new or overhaul, this Emergency AD requires a one-time borescope and visual inspections of the TRPCS assembly and bearing to determine the condition of the bearings. The actions in this Emergency AD are intended to detect a binding bearing, prevent loss of TR control, and possible loss of control of the helicopter.
This Emergency AD requires, before further flight, removing TRPCS assemblies with less than 5 hours TIS. This Emergency AD also requires, for TRPCS assemblies with 5 or more hours TIS since new or overhaul, borescope inspecting the TRPCS and bearing assemblies for damaged bearings and seals, purged grease with any metallic particles from the bearings, radial play in the bearings, and correct installation of the white Teflon seals, snap rings, and cotter pin, and determining whether there is free rotation in the angular contact bearing. These inspections are required before further flight for TRPCS assemblies that have between 5 and 15 hours TIS since new or overhaul. For TRPCS assemblies with more than 15 hours TIS, these inspections are required within 20 hours TIS or before reaching 80 hours TIS, whichever occurs first. If there is any damage to the bearings, restrictive radial play, purged grease with metallic particles, or missing or incorrect installation of the white Teflon seals, snap rings, or cotter pin, this Emergency AD requires replacing the TRPCS and bearing assembly before further flight.
Differences Between This Emergency AD and the Service Information:
The ASB requires operators to contact Sikorsky if there are any discrepancies, this Emergency AD does not. The ASB allows 20 hours TIS to perform the visual bearing inspection if the borescope inspection has already been performed, while this Emergency AD allows 20 hours TIS for TRPCS assemblies with 15 or more hours TIS.
See also |
Sikorsky S-92
FAA Federal Aviation Administration 
