The aircraft, with 242 people on board, came down shortly after taking off from the Indian city of Ahmedabad bound for Gatwick, in the world’s worst aviation disaster in a decade.
At least one person – a British national – survived the disaster and he told Indian media how he had heard a loud noise soon after the plane left the ground.
Former British Airways pilot Alastair Rosenschein is among several experts who have told Sky News about their first look at video of Flight 171 which showed some potential anomalies.
“It’s clearly got its [landing] gear down and that is not correct… it should have been up. And from the video… it’s not immensely clear… but it does look like the aircraft didn’t have its take-off flap setting.”
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Mr Rosenschein explained that the wing flaps need to be set correctly as they extend the shape of each wing and create vital extra lift at lower speeds to enable the plane to take-off and climb effectively.
He added that, while he was speculating, it “could explain why the aircraft came down” as the “aircraft would not have been able to maintain flight”.
“The video is not that clear, but it [the flaps setting] doesn’t look right to me,” he said.
“The attitude of the aircraft isn’t right either and the aircraft seems to be descending rather than climbing.
“It does look like it’s an aerodynamic issue because of not having the right flaps setting on take-off.”
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Ian Petchenik, Flightradar24’s director of communications, told the Sky News Daily podcast that he also struggled to understand how “shortly after take-off, the aircraft lost height”.
Focus on flaps and landing gear
He speculated that the aircraft suffered “possibly a flap issue” although footage of the plane just before the crash is poor quality.
He added the landing gear also “stayed down a bit longer than is usual” although there could be other reasons for that.
Mr Rosenschein also spoke about the status of the landing gear, which are usually retracted into the body of the aircraft shortly after becoming airborne.
“I cannot understand why the gear would have been down… [and] left down. That would suggest, perhaps, a hydraulic problem because it’s hydraulics that raise the gear… but this is speculation.
“The accident investigators will be looking at all the videos that are available, but they’ll get the vast majority of their information directly from the two black boxes”.
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Black boxes will be vital
India’s Aircraft Accident Investigation Bureau will be keen to access the data on the black boxes, or flight data recorders, which store essential information about the configuration of the aircraft, including the flaps and landing gear.
Paul Edwards, an aviation security analyst and fellow at the Royal Aeronautical Society, also says it remains a mystery why the landing gear was still down.
“On take-off, a pilot would bring up the wheels as quickly as possible… the aircraft is more efficient in accelerating and in the climb,” he told Sky News.
“It could have been he [the pilot] just didn’t have time, or it could be that perhaps he thought he could control it, go round again and land or even land straight ahead.”
“Really, we can’t second-guess it,” he added. “So that remains, if you like, a mystery.”
He described the Boeing 787 Dreamliner as having an “impeccable” safety record.
Dr Jason Knight, senior lecturer in fluid mechanics at the University of Portsmouth, has raised the possibility that a bird strike could be linked to the crash.
Was a bird strike to blame?
“It is very unlikely that the plane was overweight or carrying too much fuel. The aircraft is designed to be able to fly on one engine, so the most likely cause of the crash is a double engine failure,” he said.
“Because the altitude was so low, the pilot would have had very little time to do an emergency landing. The most likely cause of a double engine failure is a bird strike.”
Professor Graham Braithwaite, director of Aerospace and Aviation at Cranfield University, explained that passenger planes have an excellent safety record.
“Although take-off is a critical stage of flight, aircraft accidents are incredibly rare, especially involving modern aircraft types such as the Boeing 787.
“Take-off is a critical stage because the aircraft is still accelerating and any problem-solving requires a rapid response.”
‘Very surprising accident’
Professor John McDermid, Lloyd’s Register chair of safety at the University of York, agreed that “take-off and landing are the most dangerous phases of flight”.
But he described it as a “very surprising accident” given the levels of redundancy in aircraft systems and that they can climb with only one engine if needed.
“It’s surprising that the accident occurred before the aircraft had even got to 200 metres altitude.
“Pilots can abort take-off until quite late in the take-off roll, so it seems like the problem occurred very suddenly in the final part of the take-off roll [before the aircraft becomes airbourne], or shortly after take-off, and was sufficiently serious to be unmanageable.”
The weather will also form part of the investigation, although Paul Williams, professor of atmospheric science at the University of Reading, said conditions at the airport “appear to have been very good”.
“It was a dry and sunny day in Ahmedabad, with temperatures near 40C (104F). There was good visibility and light winds from the west.
“There is no indication at this stage that turbulence or other weather conditions were a factor in the crash.”
