Canadian air safety officials said Friday they expect the Federal Aviation Administration (FAA) to ground Sikorsky S-92 helicopters in the wake of the March 12 crash of an S-92 operated by Cougar Helicopter,

The helicopter was ferrying workers from Saint John's, Newfoundland to the Hibernia offshore oil platform when it plunged into the Atlantic Ocean 35 miles southeast of Saint John's. Seventeen crew and passengers were killed and one person was critically injured but survived.

An FAA spokesman said the agency was working on an emergency airworthiness directive related to the S-92, but declined to say if the agency would ground the helicopters.  As of mid-Monday no AD or grounding order had emerged from FAA Headquarters.

But it is reported that Sikorsky has requested all S-92 operators to ground their aircraft until a modification to the gearbox is completed. Cougar Helicopter reportedly said it was instructed by Sikorsky to ground their S-92s. “This requirement affects all S-92s operated globally and is not unique to Cougar Helicopter,” the company is quoted as saying. No similar announcement has come from the U.S. helicopter maker.

The Transportation Safety Board of Canada (TSB) said it has informed Transport Canada (TC), the National Transportation Safety Board (NTSB) and the FAA that investigators found a broken main gearbox filter bowl assembly mounting stud in the accident aircraft.

On January 28, 2009, Sikorsky Aircraft 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 stated.

Canadian accident investigators are still trying to determine what role the broken stud played in the fatal accident. Faulty studs can cause loss of oil pressure that could cause gearbox problems. Other factors are also being considered in the ongoing accident probe.

Sikorsky says there are 86 S-92s in service in 19 countries, two-thirds of which are used for offshore oil platform transport. The rest are used for search and rescue and passenger transport.