TSB Identifies Broken Main Gearbox Filter Bowl Assembly Mounting Stud on Cougar Helicopter Sikorsky S92-A

FAA to issue an emergency AD.


Shortly after beginning the initial wreckage examination -- as part of the Transportation Safety Board of Canada (TSB) investigation into the March 12, 2009, accident of a Cougar Helicopter Sikorsky S92 A off the coast of St. John's, Newfoundland, and Labrador -- the TSB immediately informed Transport Canada (TC), the National Transportation Safety Board (NTSB) and the Federal Aviation Administration (FAA) that they had found a broken main gearbox filter bowl assembly mounting stud.

On Jan. 28, 2009, the manufacturer Sikorsky Aircraft Corporation had issued an Alert Service Bulletin (ASB92-63-014) indicating that the main gearbox filter bowl assembly mounting titanium studs should be replaced with steel mounting studs. This one-time modification was to be accomplished within the next 1250 flight hours or within one year of the issue date of the ASB, whichever occurred first.

In light of TSB's discovery, the FAA will be issuing an emergency Airworthiness Directive stipulating that all operators of Sikorsky S92 A helicopters worldwide must install the improved studs in accordance with the existing ASB, before conducting any other flights.

The TSB is an independent agency that investigates marine, pipeline, railway and aviation transportation occurrences. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.

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