Ahmedabad/New Delhi, 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 spanning equipment problems, pilot error and weather conditions - will take into account what some officials said are apparent anomalies, although they added it was still too early to make a conclusion. The landing gear remained extended during the plane's brief ascent and flap components found scattered on nearby roads appeared improperly positioned for take-off, potentially robbing the aircraft of critical lift, one official said, asking not to be named. Officials confirmed on Friday they recovered one of the two black boxes from the rooftop of the hostel mess building - HT first reported on Thursday night that one black box was found - while a team from Boeing arrived in Ahmedabad to assist the investigation. Parts of the plane's two General Electric GEnx engines are being sent to the United States for analysis. "The wreckage will be moved to a storage facility for reconstruction by Air India, AAIB, the U.S. National Transportation Safety Board," an official said....