Airline’s maintenance regime will also be scrutinised as experts offer theories for cause of disaster

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.

With one black box now retrieved from the wreckage of the plane, India’s Aircraft Accident Investigation Bureau is looking at whether the plane’s engine thrust and wing flaps failed, and why the landing gear 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 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 has been recovered from the rooftop of the building, the cockpit voice recorder that could shed light on the pilots’ actions has not been found.

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 take-off 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.

While cautioning against jumping to conclusions, aviation analysts have put forward a range of theories of possible causes for the tragedy – the first fatal crash involving a Boeing 787 Dreamliner.

Dr Sonya Brown, a senior lecturer in aerospace design at the University of New South Wales, said the footage suggested the plane had stalled. “It does look to me like a significant loss of thrust. Aircraft lift is proportional to speed squared, so if you don’t have thrust and you lose speed – and radar data suggests after the initial short climb it was losing speed – you can stall,” Brown said.

What caused the lack of thrust remained unclear, Brown said.

According to some analysts’ interpretation, the video footage shows the plane’s wing flaps were not extended during takeoff. These panels on the wings of a plane can be extended to help generate lift and are key during takeoff and landing – the points in flight when most air accidents occur.

However, Brown said that even if the flaps were not deployed, a stall could still be avoided with increased thrust – adding that incorrect thrust settings due to human error could be one cause. She also noted that while the plane was modern, it was 11 years old, so the potential for inadequate maintenance could be investigated.

While pilot error is a potential avenue of any crash investigation, the Air India captain Sumeet Sabharwal and co-pilot Clive Kundar were highly experienced; Sabharwal had clocked up more than 8,000 flying hours in 22 years as a commercial airline pilot.

Questions about the plane itself are less immediate than in the aftermath of the Boeing 737 Max crashes of 2018 and 2019, which came soon after that model’s entry into service.

Although India’s aviation regulator has directed Air India to carry out safety inspections on its 33 remaining 787 fleet, the model has been flown for more than a decade by the Indian carrier and airlines worldwide, with relatively few problems.

Air India has also been ordered to carry out “additional maintenance actions” on the fleet, which is equipped with GE Aerospace engines – not the Rolls-Royce Trent 1,000 engines fitted to many 787s, which were grounded to address defects in recent years.

Neil Hansford, a former pilot and chair of the Strategic Aviation Solutions consultancy, said other theories the investigators should examine were potential sabotage, noting political tensions in Gujarat state, of which Ahmedabad is the largest city.

Contaminated fuel was another possibility, he said. The plane’s fuel tank was reportedly near-full, but Hansford said contaminants could lead to clogging. “Blocking fuel could cause an engine problem,” he said.

The 787 is a two-engine plane but is able to fly on one engine, one of many layers of redundancy – from backup power sources, computer monitoring systems such as autopilot and the ability for a plane to glide – baked into modern aviation that has made it, despite this latest tragedy, one of the statistically safest forms of transport.

But, Brown said: “All of these things are more effective if you have time, but this happened so soon after takeoff. If you had the same issue at 40,000ft, it’s very different to 400ft. There’s just not many layers of redundancy at that altitude.”