Possible causes Investigation focuses on engine thrust, wing flaps and maintenance regime

The official investigation into Air India flight AI171 is focusing on the Boeing 787's engine thrust, wing flaps and landing gear, with the airline's maintenance regime also coming under scrutiny.

- Elias Visontay Gwyn Topham

With one black box retrieved from the wreckage of the plane, the Indian government's Air Accident Investigation Branch was looking last night at whether its engine thrust and wing flaps had failed, and why the landing gear had remained open.

According to a Reuters report quoting a source with direct knowledge, investigators will also look at whether Air India was at fault, including on maintenance issues.

Flight AI171 issued a mayday call to air traffic control moments after takeoff from Ahmedabad to London on Thursday, having barely left the runway before descending and crashing into a building, killing all but one of the 242 people onboard.

While the digital flight data recorder was recovered from the roof-top of the building, the cockpit voice recorder, which could shed light on the pilots' actions, remained missing last night.

According to the Reuters source, a bird strike leading to double engine failure - which forced the miraculous landing of US Airways flight 1549 in 2009 on New York's Hudson River, and had been put forward by a range of experts as a potential explanation - was "not among the key areas of focus". CCTV footage appears to show clouds of dust at takeoff but no birds.

Teams of anti-terror experts were part of the investigation process, they said. US and UK officials were joining the India-led inquiry.