Task: Question Understanding
Input (English): Context : Cougar Helicopters Flight 91 (also known as Flight 491) was a scheduled flight of a Cougar Sikorsky S-92A (Registration C-GZCH) 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. 
Question : When did Cougar Helicopters Flight 91 occurr?
Output (English): point in time