Cougar Helicopters Flight 91[1] was a scheduled flight of a Cougar Sikorsky S-92A (Registration C-GZCH)[3] which ditched on 12 March 2009 en route to the SeaRose FPSO in the White Rose oil field and Hibernia Platform in the Hibernia oilfield off the coast of Newfoundland 55 kilometres (34 mi) east-southeast of St. John's, Newfoundland.

Flight 91 attempted to return to St. John's but went down at 9:48 a.m.[6][9][10] The aircraft was spotted, floating upside down, by a Provincial Airlines ice patrol airplane 25 minutes later.

[15][16] The damage to the airframe was severe enough to prevent immediate recovery of the wreckage as originally planned,[17] and efforts instead focused on recovering the remains of the passengers and crew.

The S-92 FDR/CVR is one box called a Multi-Purpose Flight Recorder, commonly referred to as a "combi-unit", manufactured by Penny and Giles in the United Kingdom.

The FAA had also issued Special Airworthiness Information Bulletin (SAIB) number SW-09-19 Sikorsky S92A Main Gearbox Emergency Procedures dated 19 March 2009.

Late on 23 March, Sikorsky issued a news release indicating that it had furnished replacement studs and tools to all operators and that 50 of 91 aircraft had been reworked already.

TSB disclosed at a news conference on 26 March that the flight data record indicated that oil pressure was lost, but that there was no anomaly other than the broken stud to explain that loss.

Damage analysis indicated that it struck the water belly-down and tail first with an acceleration of 20 g.[21][27] In 2003, the S-92A initially failed a FAR/JAR-29 additional oil system loss of lubrication test (sometimes called the "run dry" test) conducted to determine whether it could sustain 30-minute operation without main gearbox lubrication, failing after 10 minutes.

[32] On 16 June 2009, the FAA released an additional Airworthiness Directive, AD 2009-13-01, requiring the Rotorcraft Flight Manual for the S-92A helicopter be modified to clarify emergency procedures in the event of a main gearbox failure due to loss of oil pressure, and in particular to identify the urgency of an immediate landing in the event of an oil pressure loss.

The main blades were apparently rotating at the time of impact; however, the tail rotor drive gears were severely damaged, which would result in a loss of thrust.

[35][36] The Inquiry Commissioner took some interim measures to secure improved emergency response times in the North West Atlantic pending completion of the Commission's Report.

[37] On 23 October 2009, the European Aviation Safety Agency issued an airworthiness directive in response to the discovery of cracks in the mounting bolts of the main gearbox of S-92 helicopters operating in the North Sea.

[39] In June 2009, the sole survivor and the families of the 15 passengers who died in the accident filed a U.S lawsuit against Sikorsky and its subsidiary Keystone Helicopter Corporation.

The lawsuit alleged that Sikorsky "fraudulently misrepresented" the ability of the S-92 helicopter to run for 30 minutes after losing oil pressure, and further failed to notify operators of the severity of a similar incident in Australia in 2008.

[51] Pilot Matthew William Thomas Davis, 34, of St. John's, Newfoundland and Labrador, and First Officer Timothy Ross Lanouette, 47, of Comox, British Columbia, both died in the accident.