A preliminary report on the investigation into the Air India flight that crashed last month has answered some questions about the fatal accident but raised many more and fuelled speculation about the cause.

A preliminary investigation released last week by India's Aircraft Accident Investigation Bureau found confusion in the cockpit shortly before the June 12 crash, and raised fresh questions over the position of the critical engine fuel cutoff switches.

It can take a year, or even longer, for authorities to issue a final report detailing the likely cause of an accident and offering recommendations to prevent similar incidents in the future