Tue, Oct 18, 2011
Condition Could Result In Loss Of Tail Rotor Drive
The FAA has issued an emergency AD (2011-22-51) for Sikorsky
Aircraft Corporation (Sikorsky) Model S-70, S-70A, S-70C, S-70C(M),
and S-70C(M1) helicopters.
Sikorsky S-70 File Photo
This emergency AD was prompted by an accident that resulted from
the blockage of the internal oil passages of the intermediate
gearbox (IGB). The blockage occurred when a plug was left in the
IGB during coating of the IGB housing. The blockage caused
insufficient lubrication of the IGB, which overheated, seized-up,
and caused a fracture in the output shaft that drives the tail
rotor. This condition, if not corrected, could result in loss of
tail rotor drive and subsequent loss of control of the
helicopter.
The FAA reviewed Sikorsky Alert Service Bulletin No. 70-06-29A,
dated October 11, 2011 (ASB). The ASB specifies:
A one-time borescope inspection of the lubrication passages from
the oil scupper to the input and output housing.
Disassembling the IGB for inspection as an alternative to the
borescope inspection.
Adding an “A” suffix to the serial number of all IGBs
that have been inspected.
The FAA are issuing this AD because it evaluated all the
relevant information and determined the unsafe condition described
previously is likely to exist or develop in other products of the
same type designs.
This AD requires borescope inspecting the IGB for any
obstruction in the oil passages. As an alternative to the borescope
inspection, this AD allows disassembling the IGB and inspecting the
oil passages for any obstruction. If there is any obstruction in
any oil passage, replace the IGB with an airworthy IGB before
further flight. These actions are required before further flight
and must be accomplished in accordance with specified portions of
the ASB described previously.
This AD does not apply to the Model H-60 helicopter as it does
not have a U.S. type certificate. Also, this AD does not require
returning any parts to Sikorsky nor does it require marking the IGB
after inspection.
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