The (Canadian) Transportation Safety Board is still investigating the cause of the Cougar Flight 491 crash, which killed 17 people.

Sikorsky claims to have proven that the chances of an oil leak from the gearbox housing is extremely unlikely.

However:

The gearbox of the Sikorsky S-92A model hadn’t passed a 30 minute dry-run test which is an industry standard that required it to run for 30 minutes without oil.

The gearbox fell about 20 minutes short of the goal when it was run at moderate speeds after oil was rapidly drained.

European regulators say the test proved the helicopter could only stay in the air for “around 10 minutes after an oil loss, and question if the cooler would be the only likely source of oil leakage.

On March 12, 2009, about 0926, Atlantic Daylight Time, a Sikorsky S-92A helicopter operated by Cougar Helicopters, impacted the waters of the North Atlantic about 28 miles east of Cape Spear near St. John’s, Newfoundland. Two pilots and 16 passengers were on board. One passenger survived with serious injuries, but the other occupants were fatally injured.

The helicopter was en route from St. John’s International Airport to an offshore oil platform in the Hibernia oil field. The pilot made a MAYDAY call due to a mechanical difficulty, and was returning to St. John’s. Visual meteorological conditions prevailed at the time of the accident. The sea had 3 – 5 meter swells.