6 days ago
Air India crash preliminary report: A look at what fuel switches are designed to do & built-in safeguards
'Cut off' transition here refers to the fuel supply to the aircraft's engines being stopped, which could be one of the key reasons behind the tragedy. On 12 June, the London-bound 787-8 Dreamliner crashed within 1 minute of the departure time, right after take-off. At least 275 people died in the crash, including 241 of the 242 on board.
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
