You will be given a definition of a task first, then some input of the task.
Generate a question which can yield the answer mentioned in the input. Generated question must be answered by the answer provided in input, without using any extra knowledge.

Context : The Downend air crash occurred on 6 November 1957 when a prototype Bristol Britannia aircraft crashed in woods near Overndale Road in Downend, a suburb of Bristol, England, on its landing approach at Filton airport during a test flight.
Answer : 6 November 1957
Output:
When did Downend air crash occur?