Two stud bolts of the Sikorsky helicopter that crashed recently off the coast of Canada broke causing first a loss in oil pressure followed by a deadly crash landing on Thursday March 12, 2009 killing 17 of 18 people on board.
"I can safely say now that the stud broke in flight and the loss of oil pressure was a result of that," Mike Cunningham, the Transportation Safety Board  (TSB) of Canada's lead investigator said, "So far, we cannot find any other anomaly that would account for that loss of oil pressure. There is further analysis and work to be done on exactly how and why that stud broke."
Upon examination of the wreckage and seats, it was determined the helicopter landed at an acceleration of about 20g. On impact windows and doors flew off.  It is not known at this time whether the victims drowned or were killed in this violent impact.
"It was [...] belly first in an upright position with a tail low attitude. That's what the damage is telling us," Allan Chaulk, a TSB investigator, "We are just scratching the surface of analyzing the data we've so far collected." 
The United States Federal Aviation Administration (FAA) did issue a directive to replace the titanium studs to steel studs before any Sikorsky S92 helicopters can resume flights. So far about 30% of helicopters worldwide still need to make the update.  
Sikorsky had issued an Alert Service Bulletin to helicopter operators in January to replace the studs by 1,250 flight hours or within the year. A S-92A flight in Australia prompted the alert when it lost oil pressure and needed to make an emergency landing.
During the examination of the wreckage, TSB investigators are uncertain why two of three aircraft flotation devices did not activate to keep the aircraft from sinking. The cockpit voice and flight data recorders were operational between cruising altitude of 9,000 feet and the descent to 800 feet, and then an unexplainable electrical malfunction caused them to cease operating.

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Preliminary investigation results released on Canadian helicopter crash