MC EXPLAINER Fatal Switch: How was the fuel supply cut off mid-air in flight AI171?

Fuel switches play a crucial role in controlling the flow of fuel to the aircraft's engines. Pilots and experts have emphasised that deliberate action is required when operating these and accidental movement is highly unlikely due to their design. Each switch is flanked by protective brackets, which help prevent unintentional changes.

Moreover, a stop-lock mechanism ensures that pilots must first lift the switch before changing to one of the two positions, Run and Cutoff. This design reinforces the safety of the fuel management system.

The switches are typically only adjusted when the aircraft is on the ground. Before departure, they are used to start the engines, and after landing, they are turned off to shut them down. During flight, you would only need to move either of these switches if one of the engines fails or if it is so damaged that it's necessary to cut its fuel supply. This is crucial for maintaining flight safety.

Did the plane have faulty fuel switches?

The AAIB report points to an aircraft issue. It refers to a 2018 bulletin from the US aviation regulator on fuel switch malfunction.

"The FAA issued a Special Airworthiness Information Bulletin (SAIB) No. NM-18-33 on December 17, 2018, regarding the potential disengagement of the fuel control switch-locking feature," the AAIB report read.

The AAIB report adds that Air India did not carry out the inspection recommended in the bulletin as it was not mandatory.

"This SAIB was issued based on reports from operators of Model 737 airplanes that the fuel control switches were installed with the locking feature disengaged. The airworthiness concern was not considered an unsafe condition that would warrant an airworthiness directive (AD) by the FAA," the AAIB report added.

The report mentions that the fuel control switch design, including the locking feature, is similar on various Boeing airplane models.

"The scrutiny of maintenance records revealed that the throttle control module was replaced on VT-ANB in 2019 and 2023," the report said. The AAIB added that the reason for the replacement was not linked to the fuel control switch.

"There has been no defect reported pertaining to the fuel (throttle) control switch since 2023 on VT-ANB," the report said.

Could a pilot have mistakenly cut off the fuel?

According to the AAIB report, cockpit voice recordings revealed one pilot asking, "Why did you cut off the fuel?" and the other replied, "I did not do so."

This raises the possibility of accidental change. Aviation experts have highlighted the presence of gated switches, an important mechanical feature to prevent inadvertent change of position.

With these, an individual must first lift or pull a guard mechanism. With this extra step, gated switches enhance operational safety and help minimise the risk of unintended action.

In certain situations, such as engine failure, significant performance issues, or serious engine damage, a specific procedure needs to be followed.

When faced with these challenges, pilots are trained to shut down the affected engine. To do this, they must flip the fuel control switch associated with that engine from the Run to the Cutoff position. This immediately stops fuel supply, leading to a rapid loss of thrust from the engine in question.

The pilots may also switch off fuel supply and then switch it back on if they believe the affected engine can be restarted safely.

All this would entail adjusting just one fuel control switch, not both. Modern twin-engine aircraft are designed to fly for extended periods, sometimes several hours, on just one engine.

Furthermore in the case of Air India flight A1 171, which was in the air for only 39 seconds, pilots would have found it extremely hard to flip the fuel switches in case of a engine failure.

There has been some speculation regarding the AI 171 crash, although no official information supports it, suggesting that the aircraft may have experienced the loss of one engine during take-off. In this scenario, the pilots could have possibly misidentified the malfunctioning engine and inadvertently shut down the functioning one.

Shutting down an engine during flight is a structured and carefully considered process. Pilots are extensively trained to follow a checklist to ensure the shutdown is performed correctly. This is not an arbitrary decision made by a single pilot; it requires coordination between both pilots and is typically carried out only after the aircraft has reached a safe altitude. Despite these precautions, there have been rare instances in the past where fuel supply to the wrong engine was mistakenly cut off.

Expert opinion on the preliminary crash report 

Aviation safety expert Mark D Martin has voiced concerns regarding the preliminary report. He pointed out that the report indicates both engine fuel switches were switched to Cutoff during takeoff, which is quite unusual and warrants global attention from all operators of Boeing 787.

Martin emphasised that it is unlikely for any skilled pilot to intentionally adjust the fuel switches during such a critical phase of the flight. During takeoff, pilots are primarily focussed on crucial instruments directly in front of them, such as the landing gear and flap controls. The mid-console, where the fuel switches are located, is typically not a point of focus at this crucial time.

US aviation analyst Anthony Brickhouse also pointed out that it is very unlikely that both switches would be flipped during takeoff unless there was a specific intention or an emergency. However, no signs of an emergency, such as an engine fire, were reported or observed.

What happened onboard AI 171 before it crashed?

As per the Electronic Aircraft Flight Recorder (EAFR) data, the aircraft crossed the takeoff speed (V₁) and reached 153 knots at 08:08:33 UTC. The V-speed of 155 knots was achieved at 08:08:35 UTC, and the aircraft’s air/ground sensors confirmed liftoff at 08:08:39 UTC.

At 08:08:42, the aircraft hit its maximum recorded speed of 180 knots. Immediately after that, engine 1 and engine 2 fuel cutoff switches were moved from Run to Cutoff within a second of each other. Following this, the engine speed started dropping as the fuel supply was cut off.

The report highlighted that both engines fell below the minimum idle speed, prompting the activation of the RAT (Ram air turbine), which began supplying hydraulic power at approximately 08:08:47 UTC.

Ten seconds later, the pilots made an attempt to restart the engines.

The London-bound aircraft was in the air for only 39 seconds before crashing into the BJ Medical College hostel building, resulting in an explosion about 2 kilometres from the runway.

What will happen in the investigation moving forward?

On July 12, it was reported that investigators are now concentrating their efforts on analysing the cockpit audio to discern which pilot said what. This will help clarify the sequence of events and determine if the fuel switches were activated manually or automatically.

Additionally, the team intends to evaluate the operational status of the Dreamliner’s fuel switch system and its overall software mechanisms. This is crucial for drawing any final conclusions regarding the mid-air shutdown of both engines.

The Director General of the AAIB has formed a special investigation team. Led by Investigator-in-Charge Sanjay Kumar Singh, the team includes Chief Investigator Jasbir Singh Larhga, and team members Vipin Venu Varakoth, Veeraragavan K, and Vaishnav Vijayakumar.

To enhance the investigation, AAIB has enlisted the help of seasoned professionals, including experienced pilots, engineers, aviation medicine specialists, psychologists, and flight recorder experts. These subject matter experts (SMEs) will contribute their knowledge in their respective fields to aid the investigation.