India, June 14 -- In the twisted metal and charred debris of what was once one of India's most advanced passenger jets, investigators began on Friday the meticulous work of unravelling how 33 seconds of flight ended as the nation's deadliest aviation disaster in three decades.

As teams from India's Aircraft Accident Investigation Bureau worked through the debris of Air India flight 171 at Ahmedabad's BJ Medical College, the aviation regulator separately ordered the carrier to step up specific safety inspections --- a set of pre-flight checks of six critical aircraft systems that experts believe could indicate possible theories being explored for the air crash probe.

The probe - which will focus on a range of possibilities and scenarios ...