Task: Question Generation
Input (English): 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. 
Subject : Downend air crash 
Relation : point in time
Output (English): When did Downend air crash occur?