Detailed Instructions: You will be given a context, a subject and a relation. Your task is to generate a question based on the subject and relation. The generated question should include the given subject. Try to use a minimum number of words that are not present in either context, subject or relation while generating question.
Q: 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. 
Subject : Cougar Helicopters Flight 91 
Relation : point in time
A:
When did Cougar Helicopters Flight 91 occurr?