Image source, Reuters

As we've been reporting, the preliminary investigation into the Air India Flight 171 crash has been released.

If you are just joining us, here's what we know so far:

• According to data from the flight recorder, both the fuel control switches were moved from the run to the cut-off position shortly after takeoff, causing both engines to lose thrust and the plane to sink down
• In a voice recording of the cockpit, one of the pilots is heard asking the other why he “did the cut-off” - the other pilot is heard saying he did not do so - it was not clear which pilot made the respective remarks

• The switches were then moved back into their normal in-flight position, something which would automatically start the process of relighting the engines
• One engine was able to restart, while the other relit but failed to regain thrust
• CCTV footage from the airport showed no "significant bird activity"
• The report does not draw any conclusions, and points out that the investigation is continuing

Soutik Biswas
India Correspondent

Investigators are zeroing in on what they describe as an interesting point in the report.

The report says in December 2018, the Federal Aviation Administration (FAA) issued a Special Airworthiness Information Bulletin (SAIB) highlighting that some Boeing 737 fuel control switches were installed with the locking feature disengaged.

While the issue was noted, it wasn’t deemed an unsafe condition requiring an Airworthiness Directive - a legally enforceable regulation to correct unsafe conditions in a product.

The same switch design is used in Boeing 787-8 aircraft, including Air India’s VT-ANB, which crashed. As the SAIB was advisory, Air India did not perform the recommended inspections.

Shawn Pruchnicki, a former airline accident investigator and aviation expert at Ohio State University, tells the BBC he’s wondering whether there was a problem with the fuel control switches.

“What does this [bit in the report] exactly mean? Does it mean that with a single flip, that switch could shut the engine off and cut the fuel supply?" he says.

"When the locking feature is disengaged, what exactly happens? Could the switch just flip itself to OFF and shut down the engine? If that’s the case, it’s a really serious issue. If not, this also needs to be explained."

12 June Air India Flight 171 plane crashes shortly after take off, killing 260 people, including 241 of the 242 people on board

13 June The Indian Ministry of Civil Aviation’s investigation into the cause of the crash begins, as UK and US investigators arrive at the crash site - the first black box is also recovered on this date

16 June Second black box found in the debris at the crash site, though the exact location has not been shared

24 June Both black boxes are transported to Delhi by the Indian Air Force as the data extraction process begins

25 June Memory module and data from the black boxes is successfully downloaded and analysis to reconstruct events leading to the incident begins

12 July Thirty days on from the crash, and after 16 days of analysing the black box data the initial report is released, as outlined under international aviation rules. It finds that the fuel control switches were moved to cut-off position moments before the plane crashed

Cause of plane crash remains unresolvedpublished at 02:57 British Summer Time

02:57 BST

Soutik Biswas
India Correspondent

Investigators say there are two main takeaways from the preliminary report on Air India Flight 171.

First, both engine fuel cut off switches moved from run to cut off within seconds of takeoff, abruptly cutting the plane's thrust at 180 knots.

Cockpit voice recordings capture one pilot asking the other why they'd shut the engines down, only to be met with a denial - heightening suspicion that this wasn’t a routine or accidental action. Engineers note these switches are specifically guarded and require deliberate operation, typically reserved for emergencies like engine fire - not mid-flight manoeuvres.

Second, the preliminary findings reference a 2018 Federal Aviation Authority bulletin alerting operators to the possible disengagement of the fuel switch locking mechanism.

However, there’s no clear explanation of how this mechanical issue could have caused both switches to flip nearly simultaneously. The bulletin was advisory and inspections by Air India were skipped. The airline’s past maintenance included throttle module replacements in 2019 and 2023. None of these replacements were linked to the fuel control switches.

Until further investigation digs into whether this was human error or a rare mechanical malfunction, the cause remains unresolved.

Footage taken after the Air India plane crash in June shows smoke billowing into the air following the incident.

The London-bound Boeing 787-8 Dreamliner crashed less than a minute after taking off on 12 June from Ahmedabad airport in western India, killing 260 people, most of them passengers.

Samira Hussain
Reporting from Delhi

Two days ago, I met Shweta Parihar, 41, who lost her husband Abhinav Parihar in the crash. He was returning home to London where she and her 11-year-old son were waiting for him.

Parihar, a former NHS worker, said the ongoing investigation offers her little comfort. “We are normal people. We trusted the airline. What is the point of the investigation now?” she said, choking back tears. “We are finished.”

What pains her are the questions asked by her son. "Did he suffer when he died? How much pain was he in? Did he burn?"

Parihar says her son will never fly with Air India, who he blames for killing his father, again.

British national Vishwashkumar Ramesh was the sole survivor of the Air India crash. He escaped the wreckage through an opening in the fuselage.

After the crash, he said: "I still cannot believe how I made it out alive."

This is the moment he walked away from the crash site:

Soutik Biswas
India Correspondent

Peter Goelz, a former managing director of the US's National Transportation Safety Board (NTSB), says he’s impressed by the preliminary report.

Goelz, who has led several accident investigations, says India's Aircraft Accident Investigation Bureau, responsible for the report, "needs to be praised for preparing such a detailed preliminary report.”

“Oftentimes when dealing with such a high-profile former flag carrier of a nation, the reports are far less detailed and candid.”

“This was a very detailed report. For that the AAIB should be praised.”

As we've been reporting, India's Aircraft Accident Investigation Bureau (AAIB) has published a 15-page preliminary report. It details what happened to the Air India plane that crashed within seconds after takeoff.

"The aircraft achieved the maximum recorded airspeed of 180 Knots IAS at about 08:08:42 UTC and immediately thereafter, the Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position one after another with a time gap of 01 sec," the report says.

Then, "in the cockpit voice recording, one of the pilots is heard asking the other why did he cutoff. The other pilot responded that he did not do so."

At 08:08:52 UTC, "the Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN", and four seconds after that, "the Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN." It was now 08:08:56.

At 08:09:05, nine seconds later, one of the pilots transmitted "MAYDAY MAYDAY MAYDAY" to the Air Traffic Control Officers on the ground. The officers received no response, and shortly afterwards, they saw the plane crashing.

Here is a link, external to the preliminary report.

Archana Shukla
India business correspondent

One thing that stands out from the report is that so far there has been no advisory issued for the Boeing Dreamliner 787 or the GE GEnx-1B engine operators used in this aircraft.

At the moment mechanical fault has been ruled out but we need to wait for more information to come out as these are just preliminary findings.

The content of the report is, however, quite shocking, especially the fact that both the fuel control switches were moved from the run position to the cut-off position.

But many questions are still swirling around.

Was it a technical issue? Was it a software issue? Was it a human error?

The findings of this report are being closely watched as families of this devastating crash seek closure.

Air India has released a statement on the report. It says that the airline "stands in solidarity with the families and those affected" and that it is cooperating fully with authorities investigating the crash.

It does not address specific findings in the report.

Here is the statement:

Prior to boarding Air India Flight 171, the crew and two pilots of the flight all underwent testing to ensure they were capable of operating the aircraft.

The report states that both pilots, who were based at Mumbai, had arrived at Ahmedabad the day before the flight and had an "adequate rest period".

The crew and pilots all also underwent a breathalyser test at 06:25 local time and were found "fit to operate the flight", it added.

The report says the fuel samples that were taken from tanks used to refuel the Air India aircraft were "satisfactory".

Aviation experts had previously told the BBC that fuel contamination was a possible factor that could've caused the crash. A dual engine failure could also result from fuel contamination or clogging.

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

The report separately outlines that a "very limited amount of fuel samples" were retrieved from the APU filter and Refuel/Jettison valve of the left wing.

"The testing of these samples will be done at a suitable facility capable of carrying out the test with the limited available quantity," the report said.

The aircraft involved was a Boeing 787-8 Dreamliner, a model that was launched 14 years ago.

And we just learned from the preliminary report that - at this stage of investigation - "there are no recommended actions to B787-8 and/or GE GEnx-1B engine operators and manufacturers".

Air India operates a fleet of more than 190 planes including 58 Boeing aircraft, according to its website.

The crashed 787 Dreamliner was 11 years old and had completed more than 700 flights in the year leading up to the disaster, Flightradar24 data showed.

As we've been reporting, the preliminary report into the Air India Flight 171 crash indicated that both engines on the plane were almost simultaneously flipped from run to cut-off.

The Boeing 787 Dreamliner then began to lose thrust and sink down, before crashing in the west Indian city of Ahmedabad.

Flipping to "cut-off" almost immediately cuts the engines, and starves them of fuel.

This typically happens when a plane has arrived at its destination and the engines are turned off.

It can also occur in emergency scenarios, but the preliminary report did not indicate there was such an incident on board.

Our team is continuing to parse through the preliminary investigation into the Air India crash.

As a reminder, under international aviation rules, the investigating state has to file an initial report, detailing any findings, within 30 days of an air crash.

In a statement released last month, India's Ministry for Civil Aviation said, external the investigation has been led by India’s Aircraft Accident Investigation Bureau.

The investigation includes an aviation medicine specialist, an Air Traffic Control officer, as well as representatives from the US National Transportation Safety Board (NTSB).

The statement adds that both black box recorders were located in the days following the crash - one on the rooftop of the building of the crash site, found on 13 June, and the other in the debris on 16 June. Data extraction began on 24 June.

The ministry statement adds that “these efforts aim to reconstruct the sequence of events leading to the accident and identify contributing factors to enhance aviation safety and prevent future occurrences".

Image source, Reuters

We now know from the report that at least five buildings were destroyed when Air India Flight 171 crashed into a densely-populated residential area in the west Indian city of Ahmedabad.

"The aircraft was destroyed due to impact with the buildings on the ground and subsequent fire," the report said.

We previously reported that nearly 30 people also died on the ground after the plane hurtled down and crashed into a hostel for medical students outside the airport in Ahmedabad.

One section of the report explains how one of the engines was able to restart after transitioning to cutoff, but could not reverse the plane's deceleration.

Engine 1’s core deceleration stopped, reversed and started to progress to recovery, the report says, while Engine 2 was able to relight but "could not arrest core speed deceleration".

The CCTV obtained from the airport showed that there was no "significant bird activity" observed in the vicinity of the flight path, the report said.

Experts had previously speculated that a bird striking the airplane could have caused the plane to crash, but the report released today suggests that was likely not the case.

In its 15-page report, the Aircraft Accident Investigation Bureau (AAIB) says the wreckage site activities, including drone photography and videography, have been completed.

The wreckage itself has been moved to a secure area near the airport.

"Both engines were retrieved from the wreckage site and quarantined at a hangar in the airport," the report said.

"Components of interest for further examinations have been identified and quarantined," the report added.