Tue, Mar 24, 2009
Requires Immediate Replacement Of Gearbox Filter Bowl Mounting
Studs
As expected, on Tuesday the Federal Aviation Administration
issued an emergency airworthiness directive (EAD) grounding all
Sikorsky S-92 medium-lift transport helicopters, until titanium
mounting studs on the gearbox filter bowl assembly can be swapped
out with steel components.
"This Emergency Airworthiness Directive (AD) is prompted by the
failure of 2 main gearbox filter bowl assembly mounting studs
(studs) that were found broken during a fatal accident
investigation in Canada," reads the AD. "Prior to the accident, the
manufacturer was investigating a July 2008 incident that also
involved broken studs. In both cases, the broken studs resulted in
rapid loss of oil. The failures have been tied to fretting and
galling of the original titanium studs; therefore, we are requiring
the removal of all titanium studs and replacement with steel
studs.
"We are issuing this Emergency AD to
prevent failure of a stud which could result in rapid loss of oil,
failure of the main gearbox, and subsequent loss of control of the
helicopter."
As ANN reported earlier, Canadian authorities
issued a similar directive this weekend, in response to findings
from the Transport Safety Board's investigation into the March 12
downing of a Cougar Helicopters S-92 off the coast of
Newfoundland.
On Monday, Sikorsky said
close to half the worldwide fleet of S-92s
have already had the mounting studs replaced, and that the
helomaker expected "close to 100 percent compliance by the end of
this week." Sikorsky also stressed "no determination has been made
that the broken studs contributed to the [Cougar] accident or if
they resulted from it."
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