MANUFACTURER: Sikorsky Model S-92A
helicopters SUBJECT: Airworthiness Directive 2009-23-51
SUMMARY: This
Emergency Airworthiness Directive (AD) is prompted by reports of
cracks in the main gearbox (MGB) mounting foot pads and foot ribs.
The manufacturer is investigating the root cause of these cracks.
Contributing factors may include corrosion and the bushing press
fit in the mounting foot bolt hole. This condition, if not
detected, could result in loss of the MGB and subsequent loss of
control of the helicopter.
We have reviewed Sikorsky Alert Service Bulletin No. 92-63-020,
dated September 11, 2009 (ASB), which describes procedures for
visually inspecting the MGB assembly mounting foot pads and foot
ribs for a crack and corrosion. The ASB specifies a 10-hour
recurring visual inspection. If you suspect a crack, the ASB
specifies a fluorescent penetrant inspection (FPI) or a dye
penetrant inspection (DPI). If you find a crack, the ASB specifies
replacing the MGB before further flight. Also, the ASB specifies
treating any corrosion.
This unsafe condition is likely to exist or develop on other
helicopters of the same type design. Therefore, this AD requires
within 10 hours time-in-service (TIS), unless accomplished
previously, and thereafter at intervals not to exceed 10 hours TIS,
cleaning and inspecting each MGB assembly mounting foot pad and rib
for a crack and corrosion. If no crack is found, the AD also
requires applying a corrosion preventive compound. If you find a
crack, the AD also requires replacing the MGB before further
flight. If you find corrosion, bubbled paint, or paint
discoloration, this AD also requires you to repair the MGB before
further flight. The actions specified in this AD are interim
actions.
This rule is issued under 49 U.S.C. Section 44701 pursuant to the
authority delegated to me by the Administrator, and is effective
immediately upon receipt of this emergency AD.
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