What happened
On 12 March 2009, a Sikorsky S-92A helicopter, registration C-GZCH, departed St. John's International Airport in Newfoundland and Labrador. The aircraft, operated by Cougar Helicopters, was transporting 16 passengers and two crew members to the Hibernaxia oil production platform.
While cruising at 9,000 feet, the flight crew received a red warning indicating a critical loss of main gearbox (MGB) oil pressure. The crew immediately declared an emergency and began a descent toward St. John's. During the return flight, the oil pressure dropped to zero. As the aircraft attempted to ditch, the loss of lubrication led to the failure of the tail rotor take-off pinion, causing a loss of drive to the tail rotor and forcing the aircraft into an autorotative descent. The helicopter struck the water with a high rate of descent and a nose-high attitude. The fuselage was severely damaged and sank rapidly in 169 metres of water. Of the 18 people on board, 17 fatalities occurred due to drowning, while one passenger survived with serious injuries.
The investigation
The TSB examined the mechanical failure of the MGB and the maintenance history of the aircraft. Investigators focused on the attachment system of the MGB oil filter bowl. The investigation revealed that the titanium studs and nuts used in the assembly had suffered from galling—a form of wear caused by friction during the installation and removal of components. This damage had accumulated over multiple maintenance cycles, as the oil filter had been replaced 11 times on this specific aircraft.
Furthermore, the investigation looked into the effectiveness of the emergency flotation system and the survival conditions in the North Atlantic. It was noted that the water temperature was near freezing, which significantly reduces the time a person can hold their breath during an underwater escape.