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."

FMI: Read The Emergency AD (.pdf)