Tue, Nov 29, 2005
Model S-76A, B, and C helicopters, equipped with a main rotor hub
pilot fitting, part number 76103-08003-101 that has 1500 or more
hours time in service.
Requirement: Inspect the lower bifilar arm
assembly for a crack in the lug attachment area in accordance with
paragraphs 3.A.(1) through 3.A.(6) of the Accomplishment
Instructions of Sikorsky Alert Service Bulletin (ASB) No. 76-65-62,
dated 14 December 2004, or later FAA approved revision.
If a crack is evident on any bifilar arm assembly lug, before
further flight, replace the bifilar arm assembly with a serviceable
bifilar arm assembly.
If no cracking is evident at the initial inspection, perform a
one-time torque test. Perform the torque test and the additional
torque procedures as stated in the Accomplishment Instructions of
paragraphs 3.B.(1) through 3.B.(3) of ASB No. 76-65-62. The torque
test is not required at the recurring inspection intervals of the
lower bifilar arm assembly.
Note: FAA AD 2005-22-01 Amdt 39-14345
Inspect within 50 hours time in service after 1 December 2005, and
thereafter at intervals not to exceed 50 hours time in
This Airworthiness Directive becomes effective on 1 December
Background: The FAA received two reports before
the ASB was issued, and two subsequent reports of cracked bifilar
arm assemblies. The additional reports indicate that cracks have
become more severe. This Directive is effective for helicopters
with certain pilot fittings, and this is different to the
applicability of the ASB. Investigation has shown the root cause of
the failure is not the bifilar itself, but the mating part that
attaches the bifilar to the main rotor hub, called the pilot
fitting. This fitting is transferring the load too abruptly into
the bifilar. The frequency of reports and severity of failures
prompted this Directive. In the most recent report, all of the six
lugs had separated from the bifilar.
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