Investigators from India, the United States, and the United Kingdom will try in the coming days to determine what caused the Boeing 787-8 Dreamliner to crash shortly after takeoff, just 1.5 km from the runway at Sardar Vallabhbhai International Airport. Patel.

What exactly happened to flight AI171 between Ahmedabad and London Gatwick on Thursday will only be revealed by a detailed investigation, but the moments after takeoff are often the most difficult in aviation.

Thursday's disaster killed 241 people on board and more were reported on the ground.

It is the first time a 787-8 Dreamliner has been involved in an accident of this nature since it entered commercial service in 2011.

The BBC has spoken to aviation experts as well as India-based pilots - some of whom spoke on condition of anonymity - who regularly fly 787-8s to understand what factors could have caused the plane to crash into residential buildings in the heart of Ahmedabad just moments after takeoff.

1. It struggled to gain altitude

The 787-8 Dreamliner was piloted by Captain Sumeet Sabharwal and his co-pilot Clive Kundar. The two were highly experienced, with more than 9,000 combined flight hours; Sabharwal had more than 22 years of experience as a commercial airline pilot.

The plane was carrying 242 people as it taxied down the runway at Ahmedabad International Airport on Thursday afternoon. The plane took off at 1:39 p.m. local time (8:09 a.m. GMT), Air India said.

It was said the plane was carrying 100 tonnes of fuel – virtually a full load – as it departed Ahmedabad.

Almost immediately after takeoff, the cockpit emitted a distress signal, according to India's aviation regulator. After that, the aircraft did not respond again.

It is not clear what prompted the distress call, but the flight’s sole survivor told Indian media he heard a loud bang as the plane struggled to gain altitude.

Footage Verify shows the plane flying low over what appears to be a residential neighbourhood.

The last data transmitted shows the plane reached an altitude of 190 metres. It then descends and is hidden by trees and buildings, before a large explosion appears on the horizon.

“He wouldn’t have had time to react if he lost both engines,” a pilot said.

CCTV footage Verify showed the plane was airborne for 30 seconds.

The plane crashed in a residential area, with images showing badly damaged apartment blocks in a densely built-up area that included hospitals and government buildings.

2. Speculation of ‘extremely rare’ double engine failure

Based on videos of the plane’s brief flight, it is almost impossible to definitively determine the cause of the disaster.

A complex investigation will begin in the coming days, including a review of the plane’s black box, which records flight data, and an examination of the wreckage.

But videos that have emerged show the plane struggling to get off the ground, apparently due to a lack of thrust or power.

Some experts have speculated that a double engine failure could have occurred, an extremely rare occurrence.

Questions have been raised about whether the plane had its Ram Air Turbine (RAT) deployed, an emergency backup turbine that comes into operation when the main engines cannot generate power for essential systems.

Double-engine failures are almost unheard of. The most notable example was the 2009 “Miracle on the Hudson,” when a US Airways Airbus A320 lost both engines in a bird strike moments after takeoff from New York’s LaGuardia Airport, but glided to safety.

A senior pilot told that double-engine failure could also be caused by fuel contamination or blockage.

Aircraft engines rely on a precise fuel metering system, and if this becomes blocked, it can lead to fuel starvation and engine shutdown.

Marco Chan, a former pilot, told that, based on available footage, there is no evidence to suggest double engine failure.

Aviation expert Mohan Ranganathan told that double engine failure would be “a very, very rare incident.”

Engine manufacturer GE Aerospace said it was sending a team to India to assist in the investigation, while Boeing said it offered its full support to the airline.

3. Bird Strike

Another possibility raised by some experts is a bird strike, which can be extremely dangerous for aircraft.

In severe cases, engines can lose power if they inhale a bird, as happened in the Jeju air disaster in South Korea, which killed 179 people last year.

Experts and pilots familiar with Ahmedabad airport told that it is “famous for birds.”

“They are always there,” Ranganathan said, echoing statements, by at least three Indian pilots who have flown in and out of the airport.

The state of Gujarat, where Ahmedabad is located, recorded 462 bird strike incidents in five years, most of them at Ahmedabad airport, according to data from the Civil Aviation Ministry tabled in Parliament in December 2023.

A September 2023 Times of India report cited Airport Authority data showing 38 bird strikes in Ahmedabad in 2022-2023, a 35% increase from the previous 12 months.

In one 2009 case, a flock of seagulls was ingested at 2,700 feet, more than four times the altitude of the Air India flight. In this case, the Indian pilots had neither the altitude nor the time to maneuver.

However, one experienced pilot stated that a bird strike is not usually catastrophic “unless it affects both engines.”

4. Could the plane's wing flaps have contributed?

Three experts suggested the disaster may have happened because the plane's wing flaps were not extended during takeoff, although other pilots and analysts have cast doubt on this.

Ailerons play a vital role during takeoff, helping the aircraft generate maximum lift at low speeds.

If they are not properly extended, a fully loaded plane - with passengers, heavy fuel for a long-haul flight, and braving the heat - will struggle to take off.

In Ahmedabad, where temperatures neared 40C on Thursday, the thinner air - due to the change in density brought about by the heat - would have required a higher wing flap setting and more engine thrust, one pilot told. In such conditions, even a small setting error can have catastrophic consequences.

CCTV footage that emerged on Thursday afternoon showed the plane taking off from Ahmedabad, struggling to gain altitude, and slowly descending before crashing.

According to one of the pilots, if the plane had taken off with its flaps retracted, the 787’s takeoff configuration warning system would have warned the crew that the configuration was unsafe.

Former pilot Chan told that the footage that has emerged so far is too distorted to determine with certainty whether the flaps were extended, but said such an error would be “very rare”.

“The flaps are adjusted by the pilots themselves, before takeoff, and there are various checklists and procedures to verify the adjustment,” Chan said. “That would point to possible human error if these are not fitted correctly.”