New Delhi: Operators of Boeing Model 737 had reported to the Boeing Company that the fuel control switches installed in their aircraft have the locking mechanism disengaged—a feature that leaves room for inadvertent operation—according to a December 2018 Federal Aviation Administration (FAA) Special Airworthiness Information Bulletin.
This design of fuel control switches with the locking mechanism is also present in other Boeing models, including the 787 series. B787-8 aircraft VT-ANB, the Dreamliner that crashed, has the same component, 4TL837-3D, as confirmed in the Aircraft Accident Investigation Bureau’s (AAIB’s) preliminary report. Aircraft that run on two engines have two toggle switches for fuel control.
On 12 June, Air India Flight 171, scheduled to fly from Ahmedabad to London, tragically crashed soon after take-off, resulting in the death of all 241 individuals on board, including 229 passengers and 12 crew members. The sole survivor was passenger Vishwashkumar Ramesh, who escaped through the emergency exit. Considering people on the ground, at least 275 lives were lost.
The AAIB report refers to a cockpit conversation between the two AI 171 pilots regarding the fuel switches. Seconds after the flight took off, the Engine 1 and Engine 2 fuel switches transitioned from the ‘run’ position to the ‘cut off’ position, one after another, within a gap of one second, the report says. One of the pilots asked the other why he ‘cut off’. The latter replied that he did not.
Speaking to ThePrint, a pilot—familiar with the aircraft—explained that under no circumstances can fuel switches move on their own, and only in case of dual-engine failure, both switches are ‘cut off’ and ‘run’ in a cycle.
Experts say the fuel switches remain guarded in a locking mechanism, leaving little to no room for inadvertently applying pressure.
Moreover, the Enhanced Airborne Flight Recorders (EAFR) data of AI 171 shows the switches of both engines of AI 171 transitioned back from ‘cut off’ to ‘run’, indicating that the pilots attempted to save the aircraft seconds before the crash. One engine restarted, but the other did not.
The two-page FAA bulletin—sent to registered owners and operators of several Boeing models, including the 787 series—asked them to inspect the fuel control switch locking feature for possible disengagement. It, however, did not come with an airworthiness directive as data was limited, and the feature was considered ‘not’ unsafe.
The preliminary report on the 12 June crash mentions that Air India informed investigators that the suggested inspection did not take place for AI 171 since it was not mandatory.
The background of the bulletin, however, mentioned that fuel control switches have a locking feature, which should remain engaged to prevent “inadvertent operation that could result in unintended switch movement between the fuel supply and fuel cutoff positions”. So, when the lock is engaged, the pilot must lift the switch to change its position.
However, if the locking feature remains disengaged, the switch can move between the two positions “without lifting the switch”. The switch remains exposed to potential “inadvertent operation” and could have an “unintended consequence, such as an in-flight engine shutdown”.
(Edited by Madhurita Goswami)