Air India crash preliminary report: A look at what fuel switches are designed to do & built-in safeguards
New Delhi: The Aircraft Accident Investigation Bureau's (AAIB) preliminary report on the Air India flight 171 crash refers to a cockpit conversation between the pilots on the transition of the fuel switches from 'run' to 'cut off'. The report says that immediately after take-off, fuel switches of both Engine 1 and Engine 2 transitioned from 'run' to 'cut off' position one after another with a time gap of one second.
Speaking to ThePrint, an Air Line Pilots' Association (ALPA) of India spokesperson said there is little to no room for fuel switches to be cut off inadvertently.
The spokesperson explained, 'Each engine of the Dreamlier has its own fuel switch. They have two positions—'run' and 'off'. There are locking mechanisms in place. The locking mechanism has to be disengaged, pushed and pulled and then it locks. It can't just be moved or turned off and on by hand. The fuel switches are guarded so that they aren't pulled inadvertently. There is a proper mechanism in place and the system alerts the pilots of each move.'
The spokesperson also highlighted that such situations during take-off are far more critical than after the aircraft has reached a certain altitude, as then the pilots have more reaction time.
One of the pilots on AI 171, as per the cockpit voice recordings, stated clearly that he had not turned the fuel switches off.
All aircraft have systems in place to alert pilots in case fuel switches are turned off. The report also mentions that the CCTV footage obtained from the airport showed the Ram Air Turbine (RAT) getting deployed during the initial climb immediately after lift-off. RAT is typically deployed in emergency situations owing to loss of power in both engines or total electronic or hydraulic failure.
The Boeing 787-8 en route from Ahmedabad to London on 12 June crashed 32 seconds after being airborne, within a minute of its scheduled departure time of 1.39 pm.
The report does refer to a known Federal Aviation Administration (FAA) Special Airworthiness Information Bulletin (SAIB) on the potential disengagement of the fuel control switch locking feature. This was based on reports from operators of Model 737 airplanes that the fuel control switches were installed with the locking feature disengaged. However, this wasn't considered an unsafe condition that would warrant an airworthiness directive (AD) by the FAA and Air India didn't carry out the suggested inspections as the SAIB was an advisory and not mandatory.
This design of the fuel control switches with the same locking mechanism is also present in other Boeing models, including the 787 series. This Dreamliner had the same relevant component (4TL837-3D).
As per data from the Enhanced Airborne Flight Recorders (EAFR), within seconds, the switches for both the engines were transitioned from 'cut off' to 'run', which indicates that the pilots in the last moments had tried to save the flight from crashing.
(Edited by Viny Mishra)
Also read: What could have gone wrong? A pilot & an ex-crew member reflect on AI 171 crash & rules of takeoff
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The 787 series of aircraft was also mentioned in the FAA advisory because its switches were similar. From images of the wreckage, it would seem that was not the case with Flight AI171. Then again, deeper material analysis is underway to conclude either way.Q. What was so crucial about the FAA advisory?A. To quote a portion of it: 'The Boeing Company (Boeing) received reports from operators of Model 737 airplanes that the fuel-control switches were installed with the locking feature disengaged The fuel control switch has a locking feature to prevent inadvertent operation that could result in unintended switch movement between the fuel supply and fuel cut-off positions. In order to move the switch from one position to the other under the condition where the locking feature is engaged, it is necessary for the pilot to lift the switch up while transitioning the switch the locking feature is disengaged, the switch can be moved between the two positions without lifting the switch during transition, and the switch would be exposed to the potential of inadvertent operation. Inadvertent operation of the switch could result in an unintended consequence, such as an in-flight engine shutdown.'The advisory also says that based on the limited data at that time, it was considered not to turn it into a mandatory check for airline operators. Now, India's Directorate General of Civil Aviation (DGCA) has asked all airlines that have aircraft mentioned in that advisory to carry out an inspection and furnish a report of the findings by July Could the highly experienced pilots have accidentally shut off the fuel supply?A. 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The engine does not need full power during taxiing. So, the fuel is cut off then as well. Then there is the scenario of an engine catching fire. In such a case, the pilot might have to cut off fuel supply to that engine to save the aircraft. So the existence of the switches and the behaviour of the aircraft are not in switches are designed in a way that makes the act of turning them a deliberate, 2-3 second job. Moreover, metal guards are installed on either side of the switches to prevent accidental bumping. Some experts have also talked about failure/malfunction of a chip (microprocessor) linked to the GE engine of the Air India plane. But the report does not talk about such a thing.Q. If not a mechanical malfunction or something accidental, what other reason could be attributed to the switches turning off?A. In that case, only one possibility remains—human error. Some global aviation experts seem to be veering towards this theory. Captain Steve Scheibner, a commercial pilot and leading aviation expert with a wide following on YouTube, is of the view that the only way the switches could be off is if someone manually switched them off, and not by accident. He also points out that India's Aircraft Accident Investigation Bureau has onboarded, among others, an 'aviation psychologist'—perhaps to assess the mental health and stress levels of the Flight AI171 pilots during switches are designed in a way that it takes three fingers and a bit of force to turn them. Thus, it's being argued that it's unusual for them to change position because of cockpit vibration or turbulence. The aviation community is also often quoting the infamous Germanwings Flight 9525 crash of 2015.Q. What happened in the Germanwings crash? Are there similarities to the Air India tragedy?A. On March 24, 2015, Germanwings Flight 9525, from Barcelona to Dsseldorf, had crashed into the French Alps, killing all 150 people on board. Investigations revealed that co-pilot Andreas Lubitz intentionally caused the the captain left the cockpit, Lubitz locked him out and then deliberately set the autopilot to descend rapidly into the mountains. Despite efforts by the captain to regain entry and calls from air traffic control, Lubitz maintained control and drove the plane into the ground. It was later discovered that Lubitz had a history of severe depression and had concealed his mental health issues from his is no direct similarity of the Germanwings tragedy to the Flight AI171 crash. However, investigators and experts are drawing parallels in terms of exploring all possibilities, including pilot intent or mental state. The Airline Pilots Association of India has rejected insinuations of suicide or human error and termed such theories as biased. Their argument is also that the pilots are being made to take the fall because they are not around to defend themselves. 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