Even as the Indian government and the Aircraft Accident Investigation Bureau (AAIB) have been tight-lipped about the findings so far in the Air India Dreamliner crash investigation, indications are that the movement of the engine fuel control switches could be a key focus area for the investigators probing the catastrophic accident. According to two reports by US-based media outlets, the ongoing probe has narrowed its focus on the movement of the fuel switches — used to allow and cut fuel flow to the plane’s engines — following an analysis of the ill-fated aircraft’s black boxes. Data has been downloaded from the black boxes and is being analysed at the AAIB lab in Delhi, with assistance from the US National Transportation Safety Board (NTSB).On June 12, the aircraft — operating flight AI 171 from Ahmedabad to London Gatwick — crashed moments after take-off, killing 241 of the 242 people on board and several on the ground. This was the worst aviation disaster involving an Indian airline in at least four decades, and the first fatal crash of Boeing’s latest generation wide-body aircraft — the 787 Dreamliner — which is why the AAIB-led investigation into the accident is being watched globally. There are around 1,100 Boeing 787 aircraft operating all over the world.In the absence of any tell-tale signs of any primary cause, various theories — from a rarest-of-rare dual engine failure to major software trouble — have been doing rounds, but with no real substantiation whatsoever. Even as a preliminary report on the tragic crash is awaited, Seattle-based aviation news publication The Air Current and news agency Reuters have reported that the probe has narrowed its focus on the movement of the engine fuel control switches, which are critical components for aircraft operations. Quoting sources, the reports say that investigators are looking at whether the fuel control switches, which can instantly cut fuel supply to the aircraft engines, were moved during take-off.Emails sent to the AAIB Director General and Air India seeking comments on the matter did not immediately elicit any response.There is no clear information yet on whether the switches were actually moved, and the investigation’s focus could be on other aspects as well. It is too early to jump to any conclusion, considering aircraft are extremely sophisticated and complex machines and detailed and painstaking investigations are required to ascertain the exact cause or combination of causes. The odds that an aviation accident has a single trigger are rare, and crashes usually have a series of things that go wrong together or one leading to another.Also Read | Air India crash preliminary report: How detailed were earlier initial probe reports by AAIB?Engine fuel control switches movementsAccording to pilots and experts, the movement of these critical switches have to be deliberate actions and their accidental movement is next to impossible. The switches have brackets on either side to protect them. Additionally, there is a stop lock mechanism that requires the pilots to lift the switch before moving it from either of its positions — RUN and CUTOFF — to the other.These switches are usually moved only when the aircraft is on ground — to start the engines before departure and to shut them down after landing. Movement of either of the switches during the flight would be required only in the event of the corresponding engine failing or suffering enough damage that would require shutting off fuel supply to it to ensure flight safety. The aircraft’s black boxes — combined flight data and cockpit voice recorder units — should be able to give clarity on whether the switches were indeed moved during any stage after the aircraft initiated the take-off, along with exhaustive engine performance data.Story continues below this adThe available information from the crashed Boeing 787-8’s black boxes “cannot rule in or out improper, inadvertent or intentional actions that preceded or followed the apparent loss of thrust” suffered by the aircraft, and details around the fuel control switches could take months to be analysed, The Air Current report said. It also cautions that while the switches may be the focus of the probe, the focus may itself shift to other possibilities in the months to come. Remains of the Air India plane that crashed moments after taking off from the Ahmedabad airport. (Photo: PTI)Need for pilots to move either of the switches while airborneThis need would arise in the case of an engine failure or a major issue with the performance of an engine, or notable damage to the engine. In such eventualities, the pilots would act to shut down the problematic engine, which would require the fuel control switch corresponding to that engine being moved from RUN to CUTOFF. This would immediately cut fuel supply to the corresponding engine, resulting in an almost instant loss of thrust in it.The pilots may also switch off fuel supply and then immediately switch it on if they believe that the affected engine could be restarted safely.It is important to note here that such an action would mostly involve moving just one fuel control switch, and not both. Modern dual engine aircraft can operate for hours on a single functional engine. One of the speculative theories, although unsubstantiated by any official information, doing rounds about the AI 171 crash was that the aircraft might have possibly lost one engine upon take-off and the pilots mistakenly misidentified the problematic engine and instead shut down the working engine.Story continues below this adPilots and aviation safety experts point out that the procedure for shutting down an engine during flight is a highly methodical and well-thought-out procedure, and has a checklist that the pilots are trained to go through. It is not something that is just done randomly by a pilot. It also must involve both pilots and is usually performed only after the plane has ascended to a safe altitude. However, a mistaken shutdown of the wrong engine has happened on rare occasions in the past. Families of victims of the Air India plane crash at the DNA testing centre in Ahmedabad. (Express Photo: Bhupendra Rana)Despite the reports by The Air Current and Reuters, it would still be too early to even make that suggestion, although it would may be considered by the investigators if either of the fuel control switches were indeed moved during flight.The only possibility where both switches may be moved together, according to a pilot, would be in the case of a rarest-of-rare dual engine failure, with the pilots desperately trying to restart both engines. In such an eventuality, the movement of the switches may not be seen as a cause of the accident.What is known so farMoments after take-off, the aircraft experienced an evident loss of thrust as it climbed around 400 feet, and the air traffic control received a ‘mayday’ call from the pilots. Within a few seconds, it lost altitude and crashed into the hostel building of a medical college in the vicinity of the Ahmedabad airport.Story continues below this adFrom amateur videos of the doomed flight, it also came to light that the Ram Air Turbine (RAT), an emergency power source, was deployed moments before the tragic crash. The RAT is essentially a wind turbine located just behind the landing gear console that deploys into the airstream to generate power when primary power sources fail.The device is a last resort for providing basic power to the aircraft when everything else fails. But the RAT is more useful at higher or cruising altitudes, giving the pilots enough time to land at the closest available airfield. Neither time nor altitude was available to the pilots of flight AI-171. The plane had just lifted off the runway and was barely at an altitude of 625 feet — 400-odd feet if Ahmedabad airport’s 200-feet elevation is accounted for — before it crashed within moments.Now, a dual engine failure is the rarest-of-rare event. But if the RAT deployed, it means there was a grave emergency — either a total electrical failure, a debilitating hydraulic failure, or a dual-engine failure, or a combination of these or more factors. Whether or not both engines were not operating at the time of the crash is not known yet. But if that was indeed the case, among the first things that the investigators would look into would be whether the fuel control switches had any role to play in it.Despite nearly two weeks of the black box data being under analysis, the fact that plane maker Boeing and engine maker GE have not issued any advisory to other operators of the 787 aircraft is being seen as an indication that mechanical issues or any other dormant issue with the aircraft or engine type are not being seen as likely causes of the accident, at least for the time being.Story continues below this adA preliminary report on the crash could be released by the AAIB any day, but the extent to which it would go into the probable causes is unclear. Preliminary reports in the past have mostly been limited to laying down the facts about the aircraft and crew, establishing the series of events leading to the accident, providing some basic analysis of the aircraft accident debris and site, and listing the steps taken so far in the investigation. The final report on the crash is likely within a year.